DrSocalkwe3n/luajit
1
0
Fork 0
Code Issues Pull Requests Actions Packages Projects Releases Wiki Activity

Fix string.format for limited precision FP conversions.

Browse Source 
Enforce round-to-even semantics. #1363
This commit is contained in:
Mike Pall
2025-12-08 22:18:40 +01:00
parent 45b771bb2c
commit 7152e15489
1 changed files with 40 additions and 3 deletions
Download Patch File Download Diff File Expand all files Collapse all files

43
src/lj_strfmt_num.c
View File

@@ -169,7 +169,9 @@ static uint32_t nd_div2k(uint32_t* nd, uint32_t ndhi, uint32_t k, SFormat sf)
}
if (k > 18) {
if (STRFMT_FP(sf) == STRFMT_FP(STRFMT_T_FP_F)) {
stop1 = 63 - (int32_t)STRFMT_PREC(sf) / 9;
/* Must not limit precision here or nd_round cannot round to even.
** stop1 = 63 - (int32_t)STRFMT_PREC(sf) / 9;
*/
} else {
int32_t floorlog2 = ndhi * 29 + lj_fls(nd[ndhi]) - k;
int32_t floorlog10 = (int32_t)(floorlog2 * 0.30102999566398114);
@@ -242,6 +244,41 @@ static uint32_t nd_add_m10e(uint32_t* nd, uint32_t ndhi, uint8_t m, int32_t e)
return ndhi;
}
/* Round to even with given precision. Extra digits are not zeroed. */
static uint32_t nd_round(uint32_t* nd, uint32_t ndlo, uint32_t ndhi, int32_t e)
{
uint32_t i;
int32_t d;
char buf[9];
if (e >= 0) {
i = (uint32_t)e / 9;
d = 8 - e + (int32_t)i * 9;
} else {
int32_t f = (e - 8) / 9;
i = (uint32_t)(64 + f);
d = 8 - e + f * 9;
}
lj_strfmt_wuint9(buf, nd[i]);
if (buf[d] < '5') {
return ndhi; /* Don't round up. */
} else if (buf[d] == '5') { /* Must check for round to even. */
if (d ? (buf[d-1] & 1) : (nd[(i + 1) & 0x3f] & 1))
goto round_up; /* Round up '[13579]5.*' */
while (++d < 9) { /* Check remaining digits in buffer. */
if (buf[d] != '0')
goto round_up; /* Round up '[02468]5[^0]*'. */
}
while (i != ndlo) { /* Check remaining fraction. */
if (nd[i])
goto round_up; /* Round up '[02468]5[^0]*'. */
i = (i - 1) & 0x3f;
}
return ndhi; /* Don't round up. */
} /* else: round up.*/
round_up:
return nd_add_m10e(nd, ndhi, 5, e); /* Round up by adding 5*10^e. */
}
/* Test whether two "nd" values are equal in their most significant digits. */
static int nd_similar(uint32_t* nd, uint32_t ndhi, uint32_t* ref, MSize hilen,
MSize prec)
@@ -432,7 +469,7 @@ static char *lj_strfmt_wfnum(SBuf *sb, SFormat sf, lua_Number n, char *p)
}
if ((int32_t)(prec - nde) < (0x3f & -(int32_t)ndlo) * 9) {
/* Precision is sufficiently low as to maybe require rounding. */
ndhi = nd_add_m10e(nd, ndhi, 5, nde - prec - 1);
ndhi = nd_round(nd, ndlo, ndhi, nde - prec - 1);
nde += (hilen != ndigits_dec(nd[ndhi]));
}
nde += ndebias;
@@ -508,7 +545,7 @@ static char *lj_strfmt_wfnum(SBuf *sb, SFormat sf, lua_Number n, char *p)
/* %f (or, shortly, %g in %f style) */
if (prec < (MSize)(0x3f & -(int32_t)ndlo) * 9) {
/* Precision is sufficiently low as to maybe require rounding. */
ndhi = nd_add_m10e(nd, ndhi, 5, 0 - prec - 1);
ndhi = nd_round(nd, ndlo, ndhi, 0 - prec - 1);
}
g_format_like_f:
if ((sf & STRFMT_T_FP_E) && !(sf & STRFMT_F_ALT) && prec && width) {