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Optimize BigDecimal#to_s #519

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Merged
mrkn merged 1 commit into from
Apr 6, 2026
+31 −3
Merged

Optimize BigDecimal#to_s #519

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34 changes: 31 additions & 3 deletions ext/bigdecimal/bigdecimal.c
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Original file line number Diff line number Diff line change
Expand Up @@ -5449,10 +5449,22 @@ VpToSpecialString(Real *a, char *buf, size_t buflen, int fPlus)
return 0;
}

#define ULLTOA_BUFFER_SIZE 20
static size_t Vp_ulltoa(unsigned long long number, char *buf)
{
static const char digits[] = "0123456789";
char* tmp = buf;

do *tmp-- = digits[number % 10]; while (number /= 10);
return buf - tmp;
}

VP_EXPORT void
VpToString(Real *a, char *buf, size_t buflen, size_t fFmt, int fPlus)
/* fPlus = 0: default, 1: set ' ' before digits, 2: set '+' before digits. */
{
char ulltoa_buf[ULLTOA_BUFFER_SIZE];
char *ulltoa_buf_end = ulltoa_buf + ULLTOA_BUFFER_SIZE;
size_t i, n, ZeroSup;
DECDIG shift, m, e, nn;
char *p = buf;
Expand Down Expand Up @@ -5492,10 +5504,11 @@ VpToString(Real *a, char *buf, size_t buflen, size_t fFmt, int fPlus)
while (m) {
nn = e / m;
if (!ZeroSup || nn) {
/* The reading zero(s) */
size_t n = (size_t)snprintf(p, plen, "%lu", (unsigned long)nn);
size_t n = Vp_ulltoa(nn, ulltoa_buf_end - 1);
if (n > plen) goto overflow;
MEMCPY(p, ulltoa_buf_end - n, char, n);
ADVANCE(n);

/* as 0.00xx will be ignored. */
ZeroSup = 0; /* Set to print succeeding zeros */
}
Expand All @@ -5514,7 +5527,22 @@ VpToString(Real *a, char *buf, size_t buflen, size_t fFmt, int fPlus)
*(--p) = '\0';
++plen;
}
snprintf(p, plen, "e%"PRIdSIZE, ex);
*p = 'e';
ADVANCE(1);

if (ex < 0) {
*p = '-';
ADVANCE(1);
ex = -ex;
}

size_t ex_n = Vp_ulltoa(ex, ulltoa_buf_end - 1);
if (ex_n > plen) goto overflow;
MEMCPY(p, ulltoa_buf_end - ex_n, char, ex_n);
ADVANCE(ex_n);
*p = '\0';
ADVANCE(1);

if (fFmt) VpFormatSt(buf, fFmt);

overflow:
Expand Down