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Mod post-Grisu3 Num renderer…

…to prefer normalized forms over the shortest possible ones.

- Also, add a bit of fudging to maintain old format, such us
    collapsing into scientific form for `e > 14` and adding
    leading zero to 1-digit exponents.
- Also, toss the assert()s #YOLO
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zoffixznet committed Mar 24, 2018
1 parent 067c059 commit 8841c4241b4faa8a201b9da8f84802015257dc2f
Showing with 30 additions and 33 deletions.
  1. +30 −33 src/math/grisu.c
@@ -21,7 +21,6 @@

#include "grisu.h"
#include <stdint.h> // uint64_t etc.
#include <assert.h> // assert
#include <math.h> // ceil
#include <stdio.h> // snprintf

@@ -162,7 +161,6 @@ static int cached_pow(int exp, diy_fp *p)
static diy_fp minus(diy_fp x, diy_fp y)
{
diy_fp d; d.f = x.f - y.f; d.e = x.e;
assert(x.e == y.e && x.f >= y.f);
return d;
}

@@ -183,7 +181,6 @@ static diy_fp multiply(diy_fp x, diy_fp y)

static diy_fp normalize_diy_fp(diy_fp n)
{
assert(n.f != 0);
while(!(n.f & 0xFFC0000000000000ULL)) { n.f <<= 10; n.e -= 10; }
while(!(n.f & D64_SIGN)) { n.f <<= 1; --n.e; }
return n;
@@ -280,7 +277,6 @@ static int grisu3(double v, char *buffer, int *length, int *d_exp)
diy_fp b_minus;
diy_fp c_mk; // Cached power of ten: 10^-k
uint64_t u64 = CAST_U64(v);
assert(v > 0 && v <= 1.7976931348623157e308); // Grisu only handles strictly positive finite numbers.
if (!(u64 & D64_FRACT_MASK) && (u64 & D64_EXP_MASK) != 0) { b_minus.f = (dfp.f << 2) - 1; b_minus.e = dfp.e - 2;} // lower boundary is closer?
else { b_minus.f = (dfp.f << 1) - 1; b_minus.e = dfp.e - 1; }
b_minus.f = b_minus.f << (b_minus.e - b_plus.e);
@@ -297,20 +293,19 @@ static int grisu3(double v, char *buffer, int *length, int *d_exp)
return success;
}

// Returns length of u when written out as a string, u must be in the range of [-9999, 9999].
static int exp_len(int u)
{
if (u > 0) return u >= 1000 ? 4 : (u >= 100 ? 3 : (u >= 10 ? 2 : 1));
else if (u < 0) return u <= -1000 ? 5 : (u <= -100 ? 4 : (u <= -10 ? 3 : 2));
else return 1;
}

static int i_to_str(int val, char *str)
{
int len, i;
char *s;
char *begin = str;
if (val < 0) { *str++ = '-'; val = -val; }
if (val < 0) {
*str++ = '-';
if (val > -10)
*str++ = '0';
val = -val;
}
else
*str++ = '+';
s = str;

for(;;)
@@ -335,10 +330,9 @@ static int i_to_str(int val, char *str)
}

int dtoa_grisu3(double v, char *dst, int size) {
int d_exp, len, success, decimals, i;
int d_exp, len, success, i;
uint64_t u64 = CAST_U64(v);
char *s2 = dst;
assert(dst);

// Prehandle NaNs
if ((u64 << 1) > 0xFFE0000000000000ULL) {
@@ -364,26 +358,29 @@ int dtoa_grisu3(double v, char *dst, int size) {
// If grisu3 was not able to convert the number to a string, then use old snprintf (suboptimal).
if (!success) return snprintf(s2, size, "%.17g", v) + (int)(s2 - dst);

decimals = MIN(-d_exp, MAX(1, len-1));
if (d_exp < 0 && (len >= -d_exp || exp_len(d_exp+decimals)+1 <= exp_len(d_exp))) // Add decimal point?
{
for(i = 0; i < decimals; ++i) s2[len-i] = s2[len-i-1];
s2[len++ - decimals] = '.';
d_exp += decimals;
// Need scientific notation as well?
if (d_exp != 0) { s2[len++] = 'e'; len += i_to_str(d_exp, s2+len); }
if (d_exp < -5 || d_exp >= 14) {
for (i = 0; i < len; ++i)
s2[len-i] = s2[len-i-1];
s2[1] = '.';
d_exp += len-1;
++len;
if (d_exp !=0 ) {
s2[len++] = 'e';
len += i_to_str(d_exp, s2+len);
}
}
else if (d_exp < 0 && d_exp >= -3) // Add decimal point for numbers of form 0.000x where it's shorter?
{
for(i = 0; i < len; ++i) s2[len-d_exp-1-i] = s2[len-i-1];
s2[0] = '.';
for(i = 1; i < -d_exp; ++i) s2[i] = '0';
len += -d_exp;
else if (d_exp < 0) {
for (i = 0; i < len; ++i)
s2[len-d_exp-1-i] = s2[len-i-1];
s2[0] = '0';
s2[1] = '.';
for (i = 2; i < -d_exp; ++i)
s2[i] = '0';
len += -d_exp;
}
// Add scientific notation?
else if (d_exp < 0 || d_exp > 2) { s2[len++] = 'e'; len += i_to_str(d_exp, s2+len); }
// Add zeroes instead of scientific notation?
else if (d_exp > 0) { while(d_exp-- > 0) s2[len++] = '0'; }
else if (d_exp < 14)
while (d_exp-- > 0) s2[len++] = '0';

s2[len] = '\0'; // grisu3 doesn't null terminate, so ensure termination.
return (int)(s2+len-dst);
}

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