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sync fmt_scaled.c with OpenBSD upstream

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revision 1.24
date: 2026/06/06 23:49:25;  author: djm;  state: Exp;  lines: +28 -12;  commitid: oznzDs0MaUT3FEqO;
rearrange scan_scaled(3) ordering of multiplications and divisions
to better preserve accuracy for large exponents. From metsw24-max
via https://github.com/openssh/openssh-portable/pull/671/

ok tb@
This commit is contained in:
Damien Miller
2026-06-07 09:56:41 +10:00
parent e9916c44c1
commit 47af21eb8d
1 changed files with 27 additions and 12 deletions
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39
openbsd-compat/fmt_scaled.c
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@@ -1,4 +1,4 @@
/* $OpenBSD: fmt_scaled.c,v 1.21 2022/03/11 07:29:53 dtucker Exp $ */
/* $OpenBSD: fmt_scaled.c,v 1.25 2026/06/06 23:53:59 djm Exp $ */
/*
* Copyright (c) 2001, 2002, 2003 Ian F. Darwin. All rights reserved.
@@ -77,7 +77,7 @@ scan_scaled(char *scaled, long long *result)
{
char *p = scaled;
int sign = 0;
unsigned int i, ndigits = 0, fract_digits = 0;
unsigned int i, ndigits = 0, fract_digits = 0, muls = 0, divs = 0;
long long scale_fact = 1, whole = 0, fpart = 0;
/* Skip leading whitespace */
@@ -186,18 +186,33 @@ scan_scaled(char *scaled, long long *result)
/* scale whole part */
whole *= scale_fact;
/* truncate fpart so it doesn't overflow.
* then scale fractional part.
/*
* Scale fractional part: compute
* fpart * scale_fact / 10^(fract_digits-1)
* without intermediate overflow. scale_fact is 1024^i,
* i.e. a power of 1024 = 2^10. Interleave
* multiply-by-1024 with divide-by-10 so the running
* value stays within long long range while preserving
* precision.
*/
while (fpart >= LLONG_MAX / scale_fact ||
fpart <= LLONG_MIN / scale_fact) {
fpart /= 10;
fract_digits--;
}
fpart *= scale_fact;
if (fract_digits > 0) {
for (i = 0; i < fract_digits -1; i++)
muls = i;
divs = fract_digits > 0 ? fract_digits - 1 : 0;
while (muls > 0 && divs > 0) {
if (fpart <= LLONG_MAX / 1024) {
fpart *= 1024;
muls--;
} else {
fpart /= 10;
divs--;
}
}
while (muls > 0) {
fpart *= 1024;
muls--;
}
while (divs > 0) {
fpart /= 10;
divs--;
}
if (sign == -1)
whole -= fpart;