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In date/time functions, fix the rendering of "subsecond" and the

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computeHMS() routine to better deal with floating point
rounding errors that arise on some 32-bit systems.

FossilOrigin-Name: e46a00ae880dd12df090105498a85017d1367f88bf27d86f0b0200cf0536a906
This commit is contained in:
drh
2023-06-17 15:22:00 +00:00
parent 56a410741b
commit 0587a1a8bb
3 changed files with 15 additions and 49 deletions
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50
src/date.c
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@@ -448,56 +448,22 @@ static void computeYMD(DateTime *p){
p->validYMD = 1;
}
/* GCC (and sometimes Clang too) will sometimes be off by 1 millisecond
** in computeHMS() on 32-bit platforms with optimization enabled.
** I don't know if this is a compiler bug or a bug in the code. It is hard
** to debug because with optimization enabled, gdb skips around so much
** you cannot see what is happening, and if you try adding debug printf()s
** to the code, the problem goes away.
**
** For now, I will work around the problem by disabling optimizations in
** the computeHMS() routine.
**
** Problem seen using gcc-5.4.0, gcc-9.4.0, clang-10. Works ok on
** MSVC, clang-3.4, and clang-6.0.
**
** Whatever the problem is, it causes some answers to be off by one
** millisecond. So we get results like "2021-03-05 03:04:05.599" instead
** of the desired result of "2021-03-05 03:04:05.600".
**
** To reproduce the problem using TH3:
**
** ./th3make debug.rc -O1 -m32 cfg/c1.cfg cov1/date8.test
*/
#if SQLITE_PTRSIZE==4 && GCC_VERSION>0
#pragma GCC push_options
#pragma GCC optimize ("O0")
#endif
/*
** Compute the Hour, Minute, and Seconds from the julian day number.
*/
static void computeHMS(DateTime *p){
int s;
int day_ms, day_min; /* milliseconds, minutes into the day */
if( p->validHMS ) return;
computeJD(p);
s = (int)((p->iJD + 43200000) % 86400000);
p->s = s/1000.0;
s = (int)p->s;
p->s -= s;
p->h = s/3600;
s -= p->h*3600;
p->m = s/60;
p->s += s - p->m*60;
day_ms = (int)((p->iJD + 43200000) % 86400000);
p->s = (day_ms % 60000)/1000.0;
day_min = day_ms/60000;
p->m = day_min % 60;
p->h = day_min / 60;
p->rawS = 0;
p->validHMS = 1;
}
/* Reactivate GCC optimization */
#if SQLITE_PTRSIZE==4 && GCC_VERSION>0
#pragma GCC pop_options
#endif
/*
** Compute both YMD and HMS
*/
@@ -1160,7 +1126,7 @@ static void datetimeFunc(
zBuf[16] = '0' + (x.m)%10;
zBuf[17] = ':';
if( x.useSubsec ){
s = (int)1000.0*x.s;
s = (int)(1000.0*x.s + 0.5);
zBuf[18] = '0' + (s/10000)%10;
zBuf[19] = '0' + (s/1000)%10;
zBuf[20] = '.';
@@ -1207,7 +1173,7 @@ static void timeFunc(
zBuf[4] = '0' + (x.m)%10;
zBuf[5] = ':';
if( x.useSubsec ){
s = (int)1000.0*x.s;
s = (int)(1000.0*x.s + 0.5);
zBuf[6] = '0' + (s/10000)%10;
zBuf[7] = '0' + (s/1000)%10;
zBuf[8] = '.';