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ieee754.c
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ieee754.c
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/*
IEEE 754 portable read / write routines
IEEE 754 is the standard for floating point arithmetic, implemented by most but not all floating point
units. These functions will read / write doubles in IEE 754, regardless of the underlying representation
of the machine. They also take a flag for endian-ness.
So they should be used whenever you want to write real values in binary, portably.
By Malcolm McLean
*/
#include <stdio.h>
#include <math.h>
#include <float.h>
/*
* read a double from a stream in ieee754 format regardless of host
* encoding.
* fp - the stream
* bigendian - set to if big bytes first, clear for little bytes
* first
*
*/
double freadieee754(FILE *fp, int bigendian)
{
unsigned char buff[8];
int i;
double fnorm = 0.0;
unsigned char temp;
int sign;
int exponent;
double bitval;
int maski, mask;
int expbits = 11;
int significandbits = 52;
int shift;
double answer;
/* read the data */
for (i = 0; i < 8; i++)
buff[i] = fgetc(fp);
/* just reverse if not big-endian*/
if (!bigendian)
{
for (i = 0; i < 4; i++)
{
temp = buff[i];
buff[i] = buff[8 - i - 1];
buff[8 - i - 1] = temp;
}
}
sign = buff[0] & 0x80 ? -1 : 1;
/* exponet in raw format*/
exponent = ((buff[0] & 0x7F) << 4) | ((buff[1] & 0xF0) >> 4);
/* read inthe mantissa. Top bit is 0.5, the successive bits half*/
bitval = 0.5;
maski = 1;
mask = 0x08;
for (i = 0; i < significandbits; i++)
{
if (buff[maski] & mask)
fnorm += bitval;
bitval /= 2.0;
mask >>= 1;
if (mask == 0)
{
mask = 0x80;
maski++;
}
}
/* handle zero specially */
if (exponent == 0 && fnorm == 0)
return 0.0;
shift = exponent - ((1 << (expbits - 1)) - 1); /* exponent = shift + bias */
/* nans have exp 1024 and non-zero mantissa */
if (shift == 1024 && fnorm != 0)
return sqrt(-1.0);
/*infinity*/
if (shift == 1024 && fnorm == 0)
{
#ifdef INFINITY
return sign == 1 ? INFINITY : -INFINITY;
#endif
return (sign * 1.0) / 0.0;
}
if (shift > -1023)
{
answer = ldexp(fnorm + 1.0, shift);
return answer * sign;
}
else
{
/* denormalised numbers */
if (fnorm == 0.0)
return 0.0;
shift = -1022;
while (fnorm < 1.0)
{
fnorm *= 2;
shift--;
}
answer = ldexp(fnorm, shift);
return answer * sign;
}
}
float freadieee754f(FILE *fp, int bigendian)
{
unsigned long buff = 0;
unsigned long buff2 = 0;
unsigned long mask;
int sign;
int exponent;
int shift;
int i;
int significandbits = 23;
int expbits = 8;
double fnorm = 0.0;
double bitval;
double answer;
for(i=0;i<4;i++)
buff = (buff << 8) | fgetc(fp);
if(!bigendian)
{
for(i=0;i<4;i++)
{
buff2 <<= 8;
buff2 |= (buff & 0xFF);
buff >>= 8;
}
buff = buff2;
}
sign = (buff & 0x80000000) ? -1 : 1;
mask = 0x00400000;
exponent = (buff & 0x7F800000) >> 23;
bitval = 0.5;
for(i=0;i<significandbits;i++)
{
if(buff & mask)
fnorm += bitval;
bitval /= 2;
mask >>= 1;
}
if(exponent == 0 && fnorm == 0.0)
return 0.0f;
shift = exponent - ((1 << (expbits - 1)) - 1); /* exponent = shift + bias */
if(shift == 128 && fnorm != 0.0)
return (float) sqrt(-1.0);
if(shift == 128 && fnorm == 0.0)
{
#ifdef INFINITY
return sign == 1 ? INFINITY : -INFINITY;
#endif
return (sign * 1.0f)/0.0f;
}
if(shift > -127)
{
answer = ldexp(fnorm + 1.0, shift);
return (float) answer * sign;
}
else
{
if(fnorm == 0.0)
{
return 0.0f;
}
shift = -126;
while (fnorm < 1.0)
{
fnorm *= 2;
shift--;
}
answer = ldexp(fnorm, shift);
return (float) answer * sign;
}
}
/*
* write a double to a stream in ieee754 format regardless of host
* encoding.
* x - number to write
* fp - the stream
* bigendian - set to write big bytes first, elee write litle bytes
* first
* Returns: 0 or EOF on error
* Notes: different NaN types and negative zero not preserved.
* if the number is too big to represent it will become infinity
* if it is too small to represent it will become zero.
*/
int fwriteieee754(double x, FILE *fp, int bigendian)
{
int shift;
unsigned long sign, exp, hibits, hilong, lowlong;
double fnorm, significand;
int expbits = 11;
int significandbits = 52;
/* zero (can't handle signed zero) */
if (x == 0)
{
hilong = 0;
lowlong = 0;
goto writedata;
}
/* infinity */
if (x > DBL_MAX)
{
hilong = 1024 + ((1 << (expbits - 1)) - 1);
hilong <<= (31 - expbits);
lowlong = 0;
goto writedata;
}
/* -infinity */
if (x < -DBL_MAX)
{
hilong = 1024 + ((1 << (expbits - 1)) - 1);
hilong <<= (31 - expbits);
hilong |= (1 << 31);
lowlong = 0;
goto writedata;
}
/* NaN - dodgy because many compilers optimise out this test, but
*there is no portable isnan() */
if (x != x)
{
hilong = 1024 + ((1 << (expbits - 1)) - 1);
hilong <<= (31 - expbits);
lowlong = 1234;
goto writedata;
}
/* get the sign */
if (x < 0) { sign = 1; fnorm = -x; }
else { sign = 0; fnorm = x; }
/* get the normalized form of f and track the exponent */
shift = 0;
while (fnorm >= 2.0) { fnorm /= 2.0; shift++; }
while (fnorm < 1.0) { fnorm *= 2.0; shift--; }
/* check for denormalized numbers */
if (shift < -1022)
{
while (shift < -1022) { fnorm /= 2.0; shift++; }
shift = -1023;
}
/* out of range. Set to infinity */
else if (shift > 1023)
{
hilong = 1024 + ((1 << (expbits - 1)) - 1);
hilong <<= (31 - expbits);
hilong |= (sign << 31);
lowlong = 0;
goto writedata;
}
else
fnorm = fnorm - 1.0; /* take the significant bit off mantissa */
/* calculate the integer form of the significand */
/* hold it in a double for now */
significand = fnorm * ((1LL << significandbits) + 0.5f);
/* get the biased exponent */
exp = shift + ((1 << (expbits - 1)) - 1); /* shift + bias */
/* put the data into two longs (for convenience) */
hibits = (long)(significand / 4294967296);
hilong = (sign << 31) | (exp << (31 - expbits)) | hibits;
x = significand - hibits * 4294967296;
lowlong = (unsigned long)(significand - hibits * 4294967296);
writedata:
/* write the bytes out to the stream */
if (bigendian)
{
fputc((hilong >> 24) & 0xFF, fp);
fputc((hilong >> 16) & 0xFF, fp);
fputc((hilong >> 8) & 0xFF, fp);
fputc(hilong & 0xFF, fp);
fputc((lowlong >> 24) & 0xFF, fp);
fputc((lowlong >> 16) & 0xFF, fp);
fputc((lowlong >> 8) & 0xFF, fp);
fputc(lowlong & 0xFF, fp);
}
else
{
fputc(lowlong & 0xFF, fp);
fputc((lowlong >> 8) & 0xFF, fp);
fputc((lowlong >> 16) & 0xFF, fp);
fputc((lowlong >> 24) & 0xFF, fp);
fputc(hilong & 0xFF, fp);
fputc((hilong >> 8) & 0xFF, fp);
fputc((hilong >> 16) & 0xFF, fp);
fputc((hilong >> 24) & 0xFF, fp);
}
return ferror(fp);
}
int fwriteieee754f(float x, FILE *fp, int bigendian)
{
int shift;
unsigned long sign, exp, hibits, buff;
double fnorm, significand;
int expbits = 8;
int significandbits = 23;
/* zero (can't handle signed zero) */
if (x == 0)
{
buff = 0;
goto writedata;
}
/* infinity */
if (x > FLT_MAX)
{
buff = 128 + ((1 << (expbits - 1)) - 1);
buff <<= (31 - expbits);
goto writedata;
}
/* -infinity */
if (x < -FLT_MAX)
{
buff = 128 + ((1 << (expbits - 1)) - 1);
buff <<= (31 - expbits);
buff |= (1 << 31);
goto writedata;
}
/* NaN - dodgy because many compilers optimise out this test, but
*there is no portable isnan() */
if (x != x)
{
buff = 128 + ((1 << (expbits - 1)) - 1);
buff <<= (31 - expbits);
buff |= 1234;
goto writedata;
}
/* get the sign */
if (x < 0) { sign = 1; fnorm = -x; }
else { sign = 0; fnorm = x; }
/* get the normalized form of f and track the exponent */
shift = 0;
while (fnorm >= 2.0) { fnorm /= 2.0; shift++; }
while (fnorm < 1.0) { fnorm *= 2.0; shift--; }
/* check for denormalized numbers */
if (shift < -126)
{
while (shift < -126) { fnorm /= 2.0; shift++; }
shift = -1023;
}
/* out of range. Set to infinity */
else if (shift > 128)
{
buff = 128 + ((1 << (expbits - 1)) - 1);
buff <<= (31 - expbits);
buff |= (sign << 31);
goto writedata;
}
else
fnorm = fnorm - 1.0; /* take the significant bit off mantissa */
/* calculate the integer form of the significand */
/* hold it in a double for now */
significand = fnorm * ((1LL << significandbits) + 0.5f);
/* get the biased exponent */
exp = shift + ((1 << (expbits - 1)) - 1); /* shift + bias */
hibits = (long)(significand);
buff = (sign << 31) | (exp << (31 - expbits)) | hibits;
writedata:
/* write the bytes out to the stream */
if (bigendian)
{
fputc((buff >> 24) & 0xFF, fp);
fputc((buff >> 16) & 0xFF, fp);
fputc((buff >> 8) & 0xFF, fp);
fputc(buff & 0xFF, fp);
}
else
{
fputc(buff & 0xFF, fp);
fputc((buff >> 8) & 0xFF, fp);
fputc((buff >> 16) & 0xFF, fp);
fputc((buff >> 24) & 0xFF, fp);
}
return ferror(fp);
}