fwrite.c

#include "dt_stdio.h"
#include <errno.h>
#include <unistd.h>    // for access()
#include <fcntl.h>
#include <stdbool.h>   // true and false
#include <stdint.h>    // INT32_MIN
#include <math.h>      // isfinite, isnan
#include <stdlib.h>    // abs
#include <string.h>    // strlen, strerror
#include <zlib.h>      // for compression to .gz

#ifdef WIN32
#include <sys/types.h>
#include <sys/stat.h>
#include <io.h>
#define WRITE _write
#define CLOSE _close
#else
#define WRITE write
#define CLOSE close
#endif

#include "myomp.h"
#include "fwriteLookups.h"
#include "fwrite.h"

#define NUM_SF   15
#define SIZE_SF  1000000000000000ULL  // 10^NUM_SF

#define MIN(a,b) (((a)<(b))?(a):(b))
#define MAX(a,b) (((a)>(b))?(a):(b))

// Globals for this file only. Written once to hold parameters passed from R level.
static const char *na;                 // by default "" or if set (not recommended) then usually "NA"
static char sep;                       // comma in .csv files
static char sep2;                      // '|' within list columns. Used here to know if field should be quoted and in freadR.c to write sep2 in list columns
static char dec;                       // the '.' in the number 3.1416. In Europe often: 3,1416
static int8_t doQuote=INT8_MIN;        // whether to surround fields with double quote ". NA means 'auto' (default)
static bool qmethodEscape=false;       // when quoting fields, how to escape double quotes in the field contents (default false means to add another double quote)
static int scipen;
static bool squashDateTime=false;      // 0=ISO(yyyy-mm-dd) 1=squash(yyyymmdd)
static bool verbose=false;

extern const char *getString(const void *, int64_t);
extern int getStringLen(const void *, int64_t);
extern int getMaxStringLen(const void *, int64_t);
extern int getMaxCategLen(const void *);
extern int getMaxListItemLen(const void *, int64_t);
extern const char *getCategString(const void *, int64_t);
extern double wallclock(void);

inline void write_chars(const char *x, char **pch)
{
  // similar to C's strcpy but i) doesn't include trailing \0 and ii) moves destination along
  char *ch = *pch;
  while (*x) *ch++=*x++;
  *pch = ch;
}

void writeBool8(int8_t *col, int64_t row, char **pch)
{
  int8_t x = col[row];
  char *ch = *pch;
  *ch++ = '0'+(x==1);
  *pch = ch-(x==INT8_MIN);  // if NA then step back, to save a branch
}

void writeBool32(int32_t *col, int64_t row, char **pch)
{
  int32_t x = col[row];
  char *ch = *pch;
  if (x==INT32_MIN) {  // TODO: when na=='\0' as recommended, use a branchless writer
    write_chars(na, &ch);
  } else {
    *ch++ = '0'+x;
  }
  *pch = ch;
}

void writeBool32AsString(int32_t *col, int64_t row, char **pch)
{
  int32_t x = col[row];
  char *ch = *pch;
  if (x == INT32_MIN) {
    write_chars(na, &ch);
  } else if (x) {
    *ch++='T'; *ch++='R'; *ch++='U'; *ch++='E';
  } else {
    *ch++='F'; *ch++='A'; *ch++='L'; *ch++='S'; *ch++='E';
  }
  *pch = ch;
}

static inline void reverse(char *upp, char *low)
{
  upp--;
  while (upp>low) {
    char tmp = *upp;
    *upp = *low;
    *low = tmp;
    upp--;
    low++;
  }
}

void writeInt32(int32_t *col, int64_t row, char **pch)
{
  char *ch = *pch;
  int32_t x = col[row];
  if (x == INT32_MIN) {
    write_chars(na, &ch);
  } else {
    if (x<0) { *ch++ = '-'; x=-x; }
    // Avoid log() for speed. Write backwards then reverse when we know how long.
    char *low = ch;
    do { *ch++ = '0'+x%10; x/=10; } while (x>0);
    reverse(ch, low);
  }
  *pch = ch;
}

void writeInt64(int64_t *col, int64_t row, char **pch)
{
  char *ch = *pch;
  int64_t x = col[row];
  if (x == INT64_MIN) {
    write_chars(na, &ch);
  } else {
    if (x<0) { *ch++ = '-'; x=-x; }
    char *low = ch;
    do { *ch++ = '0'+x%10; x/=10; } while (x>0);
    reverse(ch, low);
  }
  *pch = ch;
}

/*
 * Generate fwriteLookup.h which defines sigparts, expsig and exppow that writeNumeric() that follows uses.
 * It was run once a long time ago in dev and we don't need to generate it again unless we change it.
 * Commented out and left here in the file where its result is used, in case we need it in future.
 * Reason: ldexpl may not be available on all platforms and is slower than a direct lookup when it is.
 *
void genLookups() {
  FILE *f = fopen("/tmp/fwriteLookups.h", "w");
  fprintf(f, "//\n\
// Generated by fwrite.c:genLookups()\n\
//\n\
// 3 vectors: sigparts, expsig and exppow\n\
// Includes precision higher than double; leave this compiler on this machine\n\
// to parse the literals at reduced precision.\n\
// 2^(-1023:1024) is held more accurately than double provides by storing its\n\
// exponent separately (expsig and exppow)\n\
// We don't want to depend on 'long double' (>64bit) availability to generate\n\
// these at runtime; libraries and hardware vary.\n\
// These small lookup tables are used for speed.\n\
//\n\n");
  fprintf(f, "const double sigparts[53] = {\n0.0,\n");
  for (int i=1; i<=52; i++) {
    fprintf(f, "%.40Le%s\n",ldexpl(1.0L,-i), i==52?"":",");
  }
  fprintf(f, "};\n\nconst double expsig[2048] = {\n");
  char x[2048][60];
  for (int i=0; i<2048; i++) {
    sprintf(x[i], "%.40Le", ldexpl(1.0L, i-1023));
    fprintf(f, "%.*s%s\n", (int)(strchr(x[i],'e')-x[i]), x[i], (i==2047?"":",") );
  }
  fprintf(f, "};\n\nconst int exppow[2048] = {\n");
  for (int i=0; i<2048; i++) {
    fprintf(f, "%d%s", atoi(strchr(x[i],'e')+1), (i==2047?"":",") );
  }
  fprintf(f, "};\n\n");
  fclose(f);
  return R_NilValue;
}
*/

void writeFloat64(double *col, int64_t row, char **pch)
{
  // hand-rolled / specialized for speed
  // *pch is safely the output destination with enough space (ensured via calculating maxLineLen up front)
  // technique similar to base R (format.c:formatReal and printutils.c:EncodeReal0)
  // differences/tricks :
  //   i) no buffers. writes straight to the final file buffer passed to write()
  //  ii) no C libary calls such as sprintf() where the fmt string has to be interpretted over and over
  // iii) no need to return variables or flags.  Just writes.
  //  iv) shorter, easier to read and reason with in one self contained place.
  double x = col[row];
  char *ch = *pch;
  if (!isfinite(x)) {
    if (isnan(x)) {
      write_chars(na, &ch);
    } else {
      if (x<0) *ch++ = '-';
      *ch++ = 'I'; *ch++ = 'n'; *ch++ = 'f';
    }
  } else if (x == 0.0) {
    *ch++ = '0';   // and we're done.  so much easier rather than passing back special cases
  } else {
    if (x < 0.0) { *ch++ = '-'; x = -x; }  // and we're done on sign, already written. no need to pass back sign
    union { double d; uint64_t l; } u;
    u.d = x;
    uint64_t fraction = u.l & 0xFFFFFFFFFFFFF;           // (1<<52)-1;
    uint32_t exponent = (int32_t)((u.l>>52) & 0x7FF);    // [0,2047]

    // Now sum the appropriate powers 2^-(1:52) of the fraction
    // Important for accuracy to start with the smallest first; i.e. 2^-52
    // Exact powers of 2 (1.0, 2.0, 4.0, etc) are represented precisely with fraction==0
    // Skip over tailing zeros for exactly representable numbers such 0.5, 0.75
    // Underflow here (0u-1u = all 1s) is on an unsigned type which is ok by C standards
    // sigparts[0] arranged to be 0.0 in genLookups() to enable branch free loop here
    double acc = 0;  // 'long double' not needed
    int i = 52;
    if (fraction) {
      while ((fraction & 0xFF) == 0) { fraction >>= 8; i-=8; }
      while (fraction) {
        acc += sigparts[(((fraction & 1u)^1u)-1u) & i];
        i--;
        fraction >>= 1;
      }
    }
    // 1.0+acc is in range [1.5,2.0) by IEEE754
    // expsig is in range [1.0,10.0) by design of fwriteLookups.h
    // Therefore y in range [1.5,20.0)
    // Avoids (potentially inaccurate and potentially slow) log10/log10l, pow/powl, ldexp/ldexpl
    // By design we can just lookup the power from the tables
    double y = (1.0+acc) * expsig[exponent];  // low magnitude mult
    int exp = exppow[exponent];
    if (y>=9.99999999999999) { y /= 10; exp++; }
    uint64_t l = y * SIZE_SF;  // low magnitude mult 10^NUM_SF
    // l now contains NUM_SF+1 digits as integer where repeated /10 below is accurate

    // if (verbose) Rprintf(_("\nTRACE: acc=%.20Le ; y=%.20Le ; l=%"PRIu64" ; e=%d     "), acc, y, l, exp);

    if (l%10 >= 5) l+=10; // use the last digit to round
    l /= 10;
    if (l == 0) {
      if (*(ch-1)=='-') ch--;
      *ch++ = '0';
    } else {
      // Count trailing zeros and therefore s.f. present in l
      int trailZero = 0;
      while (l%10 == 0) { l /= 10; trailZero++; }
      int sf = NUM_SF - trailZero;
      if (sf==0) {sf=1; exp++;}  // e.g. l was 9999999[5-9] rounded to 10000000 which added 1 digit

      // l is now an unsigned long that doesn't start or end with 0
      // sf is the number of digits now in l
      // exp is e<exp> were l to be written with the decimal sep after the first digit
      int dr = sf-exp-1; // how many characters to print to the right of the decimal place
      int width=0;       // field width were it written decimal format. Used to decide whether to or not.
      int dl0=0;         // how many 0's to add to the left of the decimal place before starting l
      if (dr<=0) { dl0=-dr; dr=0; width=sf+dl0; }  // 1, 10, 100, 99000
      else {
        if (sf>dr) width=sf+1;                     // 1.234 and 123.4
        else { dl0=1; width=dr+1+dl0; }            // 0.1234, 0.0001234
      }
      // So:  3.1416 => l=31416, sf=5, exp=0     dr=4; dl0=0; width=6
      //      30460  => l=3046, sf=4, exp=4      dr=0; dl0=1; width=5
      //      0.0072 => l=72, sf=2, exp=-3       dr=4; dl0=1; width=6
      if (width <= sf + (sf>1) + 2 + (abs(exp)>99?3:2) + scipen) {
        //               ^^^^ to not include 1 char for dec in -7e-04 where sf==1
        //                       ^ 2 for 'e+'/'e-'
        // decimal format ...
        ch += width-1;
        if (dr) {
          while (dr && sf) { *ch--='0'+l%10; l/=10; dr--; sf--; }
          while (dr) { *ch--='0'; dr--; }
          *ch-- = dec;
        }
        while (dl0) { *ch--='0'; dl0--; }
        while (sf) { *ch--='0'+l%10; l/=10; sf--; }
        // ch is now 1 before the first char of the field so position it afterward again, and done
        ch += width+1;
      } else {
        // scientific ...
        ch += sf;  // sf-1 + 1 for dec
        for (int i=sf; i>1; i--) {
          *ch-- = '0' + l%10;
          l /= 10;
        }
        if (sf == 1) ch--; else *ch-- = dec;
        *ch = '0' + l;
        ch += sf + (sf>1);
        *ch++ = 'e';  // lower case e to match base::write.csv
        if (exp < 0) { *ch++ = '-'; exp=-exp; }
        else { *ch++ = '+'; }  // to match base::write.csv
        if (exp < 100) {
          *ch++ = '0' + (exp / 10);
          *ch++ = '0' + (exp % 10);
        } else {
          *ch++ = '0' + (exp / 100);
          *ch++ = '0' + (exp / 10) % 10;
          *ch++ = '0' + (exp % 10);
        }
      }
    }
  }
  *pch = ch;
}

void writeComplex(Rcomplex *col, int64_t row, char **pch)
{
  Rcomplex x = col[row];
  char *ch = *pch;
  writeFloat64(&x.r, 0, &ch);
  if (!ISNAN(x.i)) {
    if (x.i >= 0.0) *ch++ = '+';  // else writeFloat64 writes the - sign
    writeFloat64(&x.i, 0, &ch);
    *ch++ = 'i';
  }
  *pch = ch;
}

// DATE/TIME

static inline void write_time(int32_t x, char **pch)
// just a helper called below by the real writers (time-only and datetime)
{
  char *ch = *pch;
  if (x<0) {  // <0 covers NA_INTEGER too (==INT_MIN checked in init.c)
    write_chars(na, &ch);
  } else {
    int hh = x/3600;
    int mm = (x - hh*3600) / 60;
    int ss = x%60;
    *ch++ = '0'+hh/10;
    *ch++ = '0'+hh%10;
    *ch++ = ':';
    ch -= squashDateTime;
    *ch++ = '0'+mm/10;
    *ch++ = '0'+mm%10;
    *ch++ = ':';
    ch -= squashDateTime;
    *ch++ = '0'+ss/10;
    *ch++ = '0'+ss%10;
  }
  *pch = ch;
}

void writeITime(int32_t *col, int64_t row, char **pch) {
  write_time(col[row], pch);
}

static inline void write_date(int32_t x, char **pch)
// just a helper called below by the two real writers (date-only and datetime)
{
  // From base ?Date :
  //  "  Dates are represented as the number of days since 1970-01-01, with negative values
  // for earlier dates. They are always printed following the rules of the current Gregorian calendar,
  // even though that calendar was not in use long ago (it was adopted in 1752 in Great Britain and its
  // colonies)  "

  // The algorithm here in data.table::fwrite was taken from civil_from_days() here :
  //   http://howardhinnant.github.io/date_algorithms.html
  // which was donated to the public domain thanks to Howard Hinnant, 2013.
  // The rebase to 1 March 0000 is inspired: avoids needing isleap() at all.
  // The only small modifications here are :
  //   1) no need for era
  //   2) impose date range of [0000-03-01, 9999-12-31]. All 3,652,365 dates tested in test 1739
  //   3) use direct lookup for mmdd rather than the math using 153, 2 and 5
  //   4) use true/false value (md/100)<3 rather than ?: branch
  // The end result is 5 lines of simple branch free integer math with no library calls.
  // as.integer(as.Date(c("0000-03-01","9999-12-31"))) == c(-719468,+2932896)

  char *ch = *pch;
  if (x< -719468 || x>2932896) {
    // NA_INTEGER<(-719468) (==INT_MIN checked in init.c)
    write_chars(na, &ch);
  } else {
    x += 719468;  // convert days from 1970-01-01 to days from 0000-03-01 (the day after 29 Feb 0000)
    int y = (x - x/1461 + x/36525 - x/146097) / 365;  // year of the preceeding March 1st
    int z =  x - y*365 - y/4 + y/100 - y/400 + 1;     // days from March 1st in year y
    int md = monthday[z];  // See fwriteLookups.h for how the 366 item lookup 'monthday' is arranged
    y += z && (md/100)<3;  // The +1 above turned z=-1 to 0 (meaning Feb29 of year y not Jan or Feb of y+1)

    ch += 7 + 2*!squashDateTime;
    *ch-- = '0'+md%10; md/=10;
    *ch-- = '0'+md%10; md/=10;
    *ch-- = '-';
    ch += squashDateTime;
    *ch-- = '0'+md%10; md/=10;
    *ch-- = '0'+md%10; md/=10;
    *ch-- = '-';
    ch += squashDateTime;
    *ch-- = '0'+y%10; y/=10;
    *ch-- = '0'+y%10; y/=10;
    *ch-- = '0'+y%10; y/=10;
    *ch   = '0'+y%10; y/=10;
    ch += 8 + 2*!squashDateTime;
  }
  *pch = ch;
}

void writeDateInt32(int32_t *col, int64_t row, char **pch) {
  write_date(col[row], pch);
}

void writeDateFloat64(double *col, int64_t row, char **pch) {
  write_date(isfinite(col[row]) ? (int)(col[row]) : INT32_MIN, pch);
}

void writePOSIXct(double *col, int64_t row, char **pch)
{
  // Write ISO8601 UTC by default to encourage ISO standards, stymie ambiguity and for speed.
  // R internally represents POSIX datetime in UTC always. Its 'tzone' attribute can be ignored.
  // R's representation ignores leap seconds too which is POSIX compliant, convenient and fast.
  // Aside: an often overlooked option for users is to start R in UTC: $ TZ='UTC' R
  // All positive integers up to 2^53 (9e15) are exactly representable by double which is relied
  // on in the ops here; number of seconds since epoch.

  double x = col[row];
  char *ch = *pch;
  if (!isfinite(x)) {
    write_chars(na, &ch);
  } else {
    int64_t xi, d, t;
    if (x>=0) {
      xi = floor(x);
      d = xi / 86400;
      t = xi % 86400;
    } else {
      // before 1970-01-01T00:00:00Z
      xi = floor(x);
      d = (xi+1)/86400 - 1;
      t = xi - d*86400;  // xi and d are both negative here; t becomes the positive number of seconds into the day
    }
    int m = ((x-xi)*10000000); // 7th digit used to round up if 9
    m += (m%10);  // 9 is numerical accuracy, 8 or less then we truncate to last microsecond
    m /= 10;
    write_date(d, &ch);
    *ch++ = 'T';
    ch -= squashDateTime;
    write_time(t, &ch);
    if (squashDateTime || (m && m%1000==0)) {
      // when squashDateTime always write 3 digits of milliseconds even if 000, for consistent scale of squash integer64
      // don't use writeInteger() because it doesn't 0 pad which we need here
      // integer64 is big enough for squash with milli but not micro; trunc (not round) micro when squash
      m /= 1000;
      *ch++ = '.';
      ch -= squashDateTime;
      *(ch+2) = '0'+m%10; m/=10;
      *(ch+1) = '0'+m%10; m/=10;
      *ch     = '0'+m;
      ch += 3;
    } else if (m) {
      // microseconds are present and !squashDateTime
      *ch++ = '.';
      *(ch+5) = '0'+m%10; m/=10;
      *(ch+4) = '0'+m%10; m/=10;
      *(ch+3) = '0'+m%10; m/=10;
      *(ch+2) = '0'+m%10; m/=10;
      *(ch+1) = '0'+m%10; m/=10;
      *ch     = '0'+m;
      ch += 6;
    }
    *ch++ = 'Z';
    ch -= squashDateTime;
  }
  *pch = ch;
}

void writeNanotime(int64_t *col, int64_t row, char **pch)
{
  int64_t x = col[row];
  char *ch = *pch;
  if (x == INT64_MIN) {
    write_chars(na, &ch);
  } else {
    int d/*days*/, s/*secs*/, n/*nanos*/;
    n = x % 1000000000;
    x /= 1000000000;
    if (x>=0 && n>=0) {
      d = x / 86400;
      s = x % 86400;
    } else {
      // before 1970-01-01T00:00:00.000000000Z
      if (n) { x--; n += 1000000000; }
      d = (x+1)/86400 - 1;
      s = x - d*86400;  // x and d are both negative here; secs becomes the positive number of seconds into the day
    }
    write_date(d, &ch);
    *ch++ = 'T';
    ch -= squashDateTime;
    write_time(s, &ch);
    *ch++ = '.';
    ch -= squashDateTime;
    for (int i=8; i>=0; i--) { *(ch+i) = '0'+n%10; n/=10; }  // always 9 digits for nanoseconds
    ch += 9;
    *ch++ = 'Z';
    ch -= squashDateTime;
  }
  *pch = ch;
}

static inline void write_string(const char *x, char **pch)
{
  char *ch = *pch;
  if (x == NULL) {
    // NA is not quoted even when quote=TRUE to distinguish from quoted "NA" value.  But going forward: ,,==NA and ,"",==empty string
    write_chars(na, &ch);
  } else {
    int8_t q = doQuote;
    if (q==INT8_MIN) { // NA means quote="auto"
      const char *tt = x;
      if (*tt=='\0') {
        // Empty strings are always quoted to distinguish from ,,==NA
        *ch++='"'; *ch++='"';   // test 1732.7 covers this (confirmed in gdb) so it's unknown why codecov claims no coverage
        *pch = ch;
        return;
      }
      while (*tt!='\0' && *tt!=sep && *tt!=sep2 && *tt!='\n' && *tt!='\r' && *tt!='"') *ch++ = *tt++;
      // Windows includes \n in its \r\n so looking for \n only is sufficient
      // sep2 is set to '\0' when no list columns are present
      if (*tt=='\0') {
        // most common case: no sep, newline or " contained in string
        *pch = ch;  // advance caller over the field already written
        return;
      }
      ch = *pch; // rewind the field written since it needs to be quoted
      q = true;
    }
    if (q==false) {
      write_chars(x, &ch);
    } else {
      *ch++ = '"';
      const char *tt = x;
      if (qmethodEscape) {
        while (*tt!='\0') {
          if (*tt=='"' || *tt=='\\') *ch++ = '\\';
          *ch++ = *tt++;
        }
      } else {
        // qmethod='double'
        while (*tt!='\0') {
          if (*tt=='"') *ch++ = '"';
          *ch++ = *tt++;
        }
      }
      *ch++ = '"';
    }
  }
  *pch = ch;
}

void writeString(const void *col, int64_t row, char **pch)
{
  write_string(getString(col, row), pch);
}

void writeCategString(const void *col, int64_t row, char **pch)
{
  write_string(getCategString(col, row), pch);
}

int init_stream(z_stream *stream) {
  stream->next_in = Z_NULL;
  stream->zalloc = Z_NULL;
  stream->zfree = Z_NULL;
  stream->opaque = Z_NULL;

  // 31 comes from : windows bits 15 | 16 gzip format
  int err = deflateInit2(stream, Z_DEFAULT_COMPRESSION, Z_DEFLATED, 31, 8, Z_DEFAULT_STRATEGY);
  return err;  // # nocov
}

int compressbuff(z_stream *stream, void* dest, size_t *destLen, const void* source, size_t sourceLen)
{
  stream->next_out = dest;
  stream->avail_out = *destLen;
  stream->next_in = (Bytef *)source; // don't use z_const anywhere; #3939
  stream->avail_in = sourceLen;
  if (verbose) DTPRINT("deflate input stream: %p %d %p %d\n", stream->next_out, (int)(stream->avail_out), stream->next_in, (int)(stream->avail_in));

  int err = deflate(stream, Z_FINISH);
  if (verbose) DTPRINT("deflate returned %d with stream->total_out==%d; Z_FINISH==%d, Z_OK==%d, Z_STREAM_END==%d\n", err, (int)(stream->total_out), Z_FINISH, Z_OK, Z_STREAM_END);
  if (err == Z_OK) {
    // with Z_FINISH, deflate must return Z_STREAM_END if correct, otherwise it's an error and we shouldn't return Z_OK (0)
    err = -9;  // # nocov
  }
  *destLen = stream->total_out;
  return err == Z_STREAM_END ? Z_OK : err;
}

void print_z_stream(const z_stream *s)   // temporary tracing function for #4099
{
  const unsigned char *byte = (unsigned char *)s;
  for (int i=0; i<sizeof(z_stream); ++i) {
    DTPRINT("%02x ", *byte++);  // not byte[i] is attempt to avoid valgrind's use-of-uninitialized, #4639, and z_stream={0} now too
  }
  DTPRINT("\n");
}

void fwriteMain(fwriteMainArgs args)
{
  double startTime = wallclock();
  double nextTime = startTime+2; // start printing progress meter in 2 sec if not completed by then

  na = args.na;
  sep = args.sep;
  sep2 = args.sep2;
  dec = args.dec;
  scipen = args.scipen;
  doQuote = args.doQuote;
  verbose = args.verbose;

  // When NA is a non-empty string, then we must quote all string fields in case they contain the na string
  // na is recommended to be empty, though
  if (na[0]!='\0' && doQuote==INT8_MIN) doQuote = true;

  qmethodEscape = args.qmethodEscape;
  squashDateTime = args.squashDateTime;

  if (args.buffMB<1 || args.buffMB>1024) STOP(_("buffMB=%d outside [1,1024]"), args.buffMB);
  size_t buffSize = (size_t)1024*1024*args.buffMB;

  int eolLen=strlen(args.eol), naLen=strlen(args.na);
  // Aside: codacy wants strnlen but strnlen is not in C99 (neither is strlen_s). To pass `gcc -std=c99 -Wall -pedantic`
  //        we'd need `#define _POSIX_C_SOURCE 200809L` before #include <string.h> but that seems a step too far
  //        and platform specific. We prefer to be pure C99.
  if (eolLen<=0) STOP(_("eol must be 1 or more bytes (usually either \\n or \\r\\n) but is length %d"), eolLen);

  if (verbose) {
    DTPRINT(_("Column writers: "));
    if (args.ncol<=50) {
      for (int j=0; j<args.ncol; j++) DTPRINT(_("%d "), args.whichFun[j]);
    } else {
      for (int j=0; j<30; j++) DTPRINT(_("%d "), args.whichFun[j]);
      DTPRINT(_("... "));
      for (int j=args.ncol-10; j<args.ncol; j++) DTPRINT(_("%d "), args.whichFun[j]);
    }
    DTPRINT(_("\nargs.doRowNames=%d args.rowNames=%d doQuote=%d args.nrow=%"PRId64" args.ncol=%d eolLen=%d\n"),
          args.doRowNames, args.rowNames, doQuote, args.nrow, args.ncol, eolLen);
  }

  // Calculate upper bound for line length. Numbers use a fixed maximum (e.g. 12 for integer) while strings find the longest
  // string in each column. Upper bound is then the sum of the columns' max widths.
  // This upper bound is required to determine a reasonable rowsPerBatch. It also saves needing to grow the buffers which
  // is especially tricky when compressing, and saves needing to check/limit the buffer writing because we know
  // up front the buffer does have sufficient capacity.
  // A large overestimate (e.g. 2-5x too big) is ok, provided it is not so large that the buffers can't be allocated.
  // Do this first so that, for example, any unsupported types in list columns happen first before opening file (which
  // could be console output) and writing column names to it.

  double t0 = wallclock();
  size_t maxLineLen = eolLen + args.ncol*(2*(doQuote!=0) + 1/*sep*/);
  if (args.doRowNames) {
    maxLineLen += args.rowNames ? getMaxStringLen(args.rowNames, args.nrow)*2 : 1+(int)log10(args.nrow);  // the width of the row number
    maxLineLen += 2*(doQuote!=0/*NA('auto') or true*/) + 1/*sep*/;
  }
  for (int j=0; j<args.ncol; j++) {
    int width = writerMaxLen[args.whichFun[j]];
    if (width==0) {
      switch(args.whichFun[j]) {
      case WF_String:
        width = getMaxStringLen(args.columns[j], args.nrow);
        break;
      case WF_CategString:
        width = getMaxCategLen(args.columns[j]);
        break;
      case WF_List:
        width = getMaxListItemLen(args.columns[j], args.nrow);
        break;
      default:
        STOP(_("Internal error: type %d has no max length method implemented"), args.whichFun[j]);  // # nocov
      }
    }
    if (args.whichFun[j]==WF_Float64 && args.scipen>0) width+=MIN(args.scipen,350); // clamp width to IEEE754 max to avoid scipen=99999 allocating buffer larger than can ever be written
    if (width<naLen) width = naLen;
    maxLineLen += width*2;  // *2 in case the longest string is all quotes and they all need to be escaped
  }
  if (verbose) DTPRINT(_("maxLineLen=%"PRIu64". Found in %.3fs\n"), (uint64_t)maxLineLen, 1.0*(wallclock()-t0));

  int f=0;
  if (*args.filename=='\0') {
    f=-1;  // file="" means write to standard output
    args.is_gzip = false; // gzip is only for file
    // eol = "\n";  // We'll use DTPRINT which converts \n to \r\n inside it on Windows
  } else {
#ifdef WIN32
    f = _open(args.filename, _O_WRONLY | _O_BINARY | _O_CREAT | (args.append ? _O_APPEND : _O_TRUNC), _S_IWRITE);
    // O_BINARY rather than O_TEXT for explicit control and speed since it seems that write() has a branch inside it
    // to convert \n to \r\n on Windows when in text mode not not when in binary mode.
#else
    f = open(args.filename, O_WRONLY | O_CREAT | (args.append ? O_APPEND : O_TRUNC), 0666);
    // There is no binary/text mode distinction on Linux and Mac
#endif
    if (f == -1) {
      // # nocov start
      int erropen = errno;
      STOP(access( args.filename, F_OK ) != -1 ?
           _("%s: '%s'. Failed to open existing file for writing. Do you have write permission to it? Is this Windows and does another process such as Excel have it open?") :
           _("%s: '%s'. Unable to create new file for writing (it does not exist already). Do you have permission to write here, is there space on the disk and does the path exist?"),
           strerror(erropen), args.filename);
      // # nocov end
    }
  }

  int yamlLen = strlen(args.yaml);
  if (verbose) {
    DTPRINT(_("Writing bom (%s), yaml (%d characters) and column names (%s) ... "),
            args.bom?"true":"false", yamlLen, args.colNames?"true":"false");
    if (f==-1) DTPRINT(_("\n"));
  }
  size_t headerLen = 0;
  if (args.bom) headerLen += 3;
  headerLen += yamlLen;
  if (args.colNames) {
    for (int j=0; j<args.ncol; j++) headerLen += getStringLen(args.colNames, j)*2;  // *2 in case quotes are escaped or doubled
    headerLen += args.ncol*(1/*sep*/+(doQuote!=0)*2) + eolLen + 3;  // 3 in case doRowNames and doQuote (the first blank <<"",>> column name)
  }
  if (headerLen) {
    char *buff = malloc(headerLen);
    if (!buff) STOP(_("Unable to allocate %d MiB for header: %s"), headerLen / 1024 / 1024, strerror(errno));
    char *ch = buff;
    if (args.bom) {*ch++=(char)0xEF; *ch++=(char)0xBB; *ch++=(char)0xBF; }  // 3 appears above (search for "bom")
    memcpy(ch, args.yaml, yamlLen);
    ch += yamlLen;
    if (args.colNames) {
      if (args.doRowNames) {
        // Unusual: the extra blank column name when row_names are added as the first column
        if (doQuote!=0/*'auto'(NA) or true*/) { *ch++='"'; *ch++='"'; } // to match write.csv
        *ch++ = sep;
      }
      for (int j=0; j<args.ncol; j++) {
        writeString(args.colNames, j, &ch);
        *ch++ = sep;
      }
      ch--; // backup over the last sep
      write_chars(args.eol, &ch);
    }
    if (f==-1) {
      *ch = '\0';
      DTPRINT(buff);
      free(buff);
    } else {
      int ret1=0, ret2=0;
      if (args.is_gzip) {
        z_stream stream = {0};
        if(init_stream(&stream)) {
          free(buff);                                    // # nocov
          STOP(_("Can't allocate gzip stream structure"));  // # nocov
        }
        if (verbose) {DTPRINT("z_stream for header (1): "); print_z_stream(&stream);}
        size_t zbuffSize = deflateBound(&stream, headerLen);
        char *zbuff = malloc(zbuffSize);
        if (!zbuff) {
          free(buff);                                                                                   // # nocov
          STOP(_("Unable to allocate %d MiB for zbuffer: %s"), zbuffSize / 1024 / 1024, strerror(errno));  // # nocov
        }
        size_t zbuffUsed = zbuffSize;
        ret1 = compressbuff(&stream, zbuff, &zbuffUsed, buff, (size_t)(ch-buff));
        if (verbose) {DTPRINT("z_stream for header (2): "); print_z_stream(&stream);}
        if (ret1==Z_OK) ret2 = WRITE(f, zbuff, (int)zbuffUsed);
        deflateEnd(&stream);
        free(zbuff);
      } else {
        ret2 = WRITE(f,  buff, (int)(ch-buff));
      }
      free(buff);
      if (ret1 || ret2==-1) {
        // # nocov start
        int errwrite = errno; // capture write errno now incase close fails with a different errno
        CLOSE(f);
        if (ret1) STOP(_("Compress gzip error: %d"), ret1);
        else      STOP(_("%s: '%s'"), strerror(errwrite), args.filename);
        // # nocov end
      }
    }
  }
  if (verbose) DTPRINT(_("done in %.3fs\n"), 1.0*(wallclock()-t0));
  if (args.nrow == 0) {
    if (verbose) DTPRINT(_("No data rows present (nrow==0)\n"));
    if (f!=-1 && CLOSE(f)) STOP(_("%s: '%s'"), strerror(errno), args.filename);
    return;
  }

  // Writing rows

  // Decide buffer size and rowsPerBatch for each thread
  // Once rowsPerBatch is decided it can't be changed
  int rowsPerBatch=0;
  if (maxLineLen*2>buffSize) { buffSize=2*maxLineLen; rowsPerBatch=2; }
  else rowsPerBatch = buffSize / maxLineLen;
  if (rowsPerBatch > args.nrow) rowsPerBatch = args.nrow;
  if (rowsPerBatch < 1) rowsPerBatch = 1;
  int numBatches = (args.nrow-1)/rowsPerBatch + 1;
  int nth = args.nth;
  if (numBatches < nth) nth = numBatches;
  if (verbose) {
    DTPRINT(_("Writing %"PRId64" rows in %d batches of %d rows (each buffer size %dMB, showProgress=%d, nth=%d)\n"),
            args.nrow, numBatches, rowsPerBatch, args.buffMB, args.showProgress, nth);
  }
  t0 = wallclock();

  bool hasPrinted = false;
  int maxBuffUsedPC = 0;

  // compute zbuffSize which is the same for each thread
  size_t zbuffSize = 0;
  if(args.is_gzip){
    z_stream stream = {0};
    if(init_stream(&stream))
      STOP(_("Can't allocate gzip stream structure")); // # nocov
    zbuffSize = deflateBound(&stream, buffSize);
    deflateEnd(&stream);
  }

  errno=0;
  char *buffPool = malloc(nth*(size_t)buffSize);
  if (!buffPool) {
    // # nocov start
    STOP("Unable to allocate %d MB * %d thread buffers; '%d: %s'. Please read ?fwrite for nThread, buffMB and verbose options.",
         (size_t)buffSize/(1024^2), nth, errno, strerror(errno));
    // # nocov end
  }
  char *zbuffPool = NULL;
  if (args.is_gzip) {
    zbuffPool = malloc(nth*(size_t)zbuffSize);
    if (!zbuffPool) {
      // # nocov start
      free(buffPool);
      STOP("Unable to allocate %d MB * %d thread compressed buffers; '%d: %s'. Please read ?fwrite for nThread, buffMB and verbose options.",
         (size_t)zbuffSize/(1024^2), nth, errno, strerror(errno));
      // # nocov end
    }
  }

  bool failed = false;   // naked (unprotected by atomic) write to bool ok because only ever write true in this special paradigm
  int failed_compress = 0; // the first thread to fail writes their reason here when they first get to ordered section
  char failed_msg[1001] = "";  // to hold zlib's msg; copied out of zlib in ordered section just in case the msg is allocated within zlib
  int failed_write = 0;    // same. could use +ve and -ve in the same code but separate it out to trace Solaris problem, #3931

  if (nth>1) verbose=false; // printing isn't thread safe (there's a temporary print in compressbuff for tracing solaris; #4099)

  #pragma omp parallel num_threads(nth)
  {
    int me = omp_get_thread_num();
    int my_failed_compress = 0;
    char *ch, *myBuff;
    ch = myBuff = buffPool + me*buffSize;

    void *myzBuff = NULL;
    size_t myzbuffUsed = 0;
    z_stream mystream = {0};
    if (args.is_gzip) {
      myzBuff = zbuffPool + me*zbuffSize;
      if (init_stream(&mystream)) { // this should be thread safe according to zlib documentation
        failed = true;              // # nocov
        my_failed_compress = -998;  // # nocov
      }
      if (verbose) {DTPRINT("z_stream for data (1): "); print_z_stream(&mystream);}
    }

    #pragma omp for ordered schedule(dynamic)
    for(int64_t start=0; start<args.nrow; start+=rowsPerBatch) {
      if (failed) continue;  // Not break. Because we don't use #omp cancel yet.
      int64_t end = ((args.nrow - start)<rowsPerBatch) ? args.nrow : start + rowsPerBatch;
      for (int64_t i=start; i<end; i++) {
        // Tepid starts here (once at beginning of each per line)
        if (args.doRowNames) {
          if (args.rowNames==NULL) {
            if (doQuote!=0/*NA'auto' or true*/) *ch++='"';
            int64_t rn = i+1;
            writeInt64(&rn, 0, &ch);
            if (doQuote!=0) *ch++='"';
          } else {
            writeString(args.rowNames, i, &ch);
          }
          *ch++=sep;
        }
        // Hot loop
        for (int j=0; j<args.ncol; j++) {
          (args.funs[args.whichFun[j]])(args.columns[j], i, &ch);
          *ch++ = sep;
        }
        // Tepid again (once at the end of each line)
        ch--;  // backup onto the last sep after the last column. ncol>=1 because 0-columns was caught earlier.
        write_chars(args.eol, &ch);  // overwrite last sep with eol instead
      }
      // compress buffer if gzip
      if (args.is_gzip && !failed) {
        myzbuffUsed = zbuffSize;
        if (verbose) {DTPRINT("z_stream for data (2): "); print_z_stream(&mystream);}
        int ret = compressbuff(&mystream, myzBuff, &myzbuffUsed, myBuff, (size_t)(ch-myBuff));
        if (verbose) {DTPRINT("z_stream for data (3): "); print_z_stream(&mystream);}
        if (ret) { failed=true; my_failed_compress=ret; }
        else deflateReset(&mystream);
      }
      #pragma omp ordered
      {
        if (failed) {
          // # nocov start
          if (failed_compress==0 && my_failed_compress!=0) {
            failed_compress = my_failed_compress;
            if (mystream.msg!=NULL) strncpy(failed_msg, mystream.msg, 1000); // copy zlib's msg for safe use after deflateEnd just in case zlib allocated the message
          }
          // else another thread could have failed below while I was working or waiting above; their reason got here first
          // # nocov end
        } else {
          errno=0;
          if (f==-1) {
            *ch='\0';  // standard C string end marker so DTPRINT knows where to stop
            DTPRINT(myBuff);
          } else if ((args.is_gzip ? WRITE(f, myzBuff, (int)myzbuffUsed)
                                   : WRITE(f, myBuff,  (int)(ch-myBuff))) == -1) {
            failed=true;         // # nocov
            failed_write=errno;  // # nocov
          }

          int used = 100*((double)(ch-myBuff))/buffSize;  // percentage of original buffMB
          if (used > maxBuffUsedPC) maxBuffUsedPC = used;
          double now;
          if (me==0 && args.showProgress && (now=wallclock())>=nextTime && !failed) {
            // See comments above inside the f==-1 clause.
            // Not only is this ordered section one-at-a-time but we'll also Rprintf() here only from the
            // master thread (me==0) and hopefully this will work on Windows. If not, user should set
            // showProgress=FALSE until this can be fixed or removed.
            // # nocov start
            int ETA = (int)((args.nrow-end)*((now-startTime)/end));
            if (hasPrinted || ETA >= 2) {
              if (verbose && !hasPrinted) DTPRINT("\n");
              DTPRINT("\rWritten %.1f%% of %"PRId64" rows in %d secs using %d thread%s. "
                      "maxBuffUsed=%d%%. ETA %d secs.      ",
                       (100.0*end)/args.nrow, args.nrow, (int)(now-startTime), nth, nth==1?"":"s",
                       maxBuffUsedPC, ETA);
              // TODO: use progress() as in fread
              nextTime = now+1;
              hasPrinted = true;
            }
            // # nocov end
          }
          // May be possible for master thread (me==0) to call R_CheckUserInterrupt() here.
          // Something like:
          // if (me==0) {
          //   failed = TRUE;  // inside ordered here; the slaves are before ordered and not looking at 'failed'
          //   R_CheckUserInterrupt();
          //   failed = FALSE; // no user interrupt so return state
          // }
          // But I fear the slaves will hang waiting for the master (me==0) to complete the ordered
          // section which may not happen if the master thread has been interrupted. Rather than
          // seeing failed=TRUE and falling through to free() and close() as intended.
          // Could register a finalizer to free() and close() perhaps :
          // [r-devel] http://r.789695.n4.nabble.com/checking-user-interrupts-in-C-code-tp2717528p2717722.html
          // Conclusion for now: do not provide ability to interrupt.
          // write() errors and malloc() fails will be caught and cleaned up properly, however.
          ch = myBuff;  // back to the start of my buffer ready to fill it up again
        }
      }
    }
    // all threads will call this free on their buffer, even if one or more threads had malloc
    // or realloc fail. If the initial malloc failed, free(NULL) is ok and does nothing.
    if (args.is_gzip) {
      deflateEnd(&mystream);
    }
  }
  free(buffPool);
  free(zbuffPool);

  // Finished parallel region and can call R API safely now.
  if (hasPrinted) {
    // # nocov start
    if (!failed) { // clear the progress meter
      DTPRINT("\r                                                                       "
              "                                                              \r");
    } else {       // don't clear any potentially helpful output before error
      DTPRINT(_("\n"));
    }
    // # nocov end
  }

  if (f!=-1 && CLOSE(f) && !failed)
    STOP(_("%s: '%s'"), strerror(errno), args.filename);  // # nocov
  // quoted '%s' in case of trailing spaces in the filename
  // If a write failed, the line above tries close() to clean up, but that might fail as well. So the
  // '&& !failed' is to not report the error as just 'closing file' but the next line for more detail
  // from the original error.
  if (failed) {
    // # nocov start
    if (failed_compress)
      STOP(_("zlib %s (zlib.h %s) deflate() returned error %d with z_stream->msg==\"%s\" Z_FINISH=%d Z_BLOCK=%d. %s"),
           zlibVersion(), ZLIB_VERSION, failed_compress, failed_msg, Z_FINISH, Z_BLOCK,
           verbose ? _("Please include the full output above and below this message in your data.table bug report.")
                   : _("Please retry fwrite() with verbose=TRUE and include the full output with your data.table bug report."));
    if (failed_write)
      STOP("%s: '%s'", strerror(failed_write), args.filename);
    // # nocov end
  }
}