starred/qemu
1
0
Fork 0
mirror of https://github.com/qemu/qemu.git synced 2026-07-08 17:46:10 +00:00
Code Issues 380 Packages Projects Releases Wiki Activity

fpu: Restrict parts_round_to_int_normal to target precision

Browse Source 
Currently parts_round_to_int_normal() assumes that its input has just
been unpacked and therefore doesn't expect non-zero fraction bits past
target precision.

The upcoming DIVIDE TO INTEGER use cases needs it to support
calculations on intermediate values that utilize all fraction bits,
while at the same time restricting the result's precision to frac_size.

Delete the "All integral" check, because even though really large
values are always integer, their low fraction bits still need to be
truncated. For the same reason, make sure rnd_mask covers at least
fraction bits past target precision.

Signed-off-by: Ilya Leoshkevich <iii@linux.ibm.com>
Reviewed-by: Thomas Huth <thuth@redhat.com>
Message-ID: <20260210214044.1174699-4-iii@linux.ibm.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>
This commit is contained in:
Ilya Leoshkevich
2026-02-10 22:39:02 +01:00
committed by Thomas Huth
parent f5682b9dee
commit b4a85d8fe7
1 changed files with 6 additions and 6 deletions
Download Patch File Download Diff File Expand all files Collapse all files

12
fpu/softfloat-parts.c.inc
View File

@@ -1118,11 +1118,6 @@ static bool partsN(round_to_int_normal)(FloatPartsN *a, FloatRoundMode rmode,
return true;
}
if (a->exp >= frac_size) {
/* All integral */
return false;
}
if (N > 64 && a->exp < N - 64) {
/*
* Rounding is not in the low word -- shift lsb to bit 2,
@@ -1132,8 +1127,13 @@ static bool partsN(round_to_int_normal)(FloatPartsN *a, FloatRoundMode rmode,
frac_shrjam(a, shift_adj);
frac_lsb = 1 << 2;
} else {
/*
* Rounding is in the low word -- compute the lsb offset for rounding
* and for clamping to the target precision, then map it to an offset
* within frac_lo.
*/
shift_adj = 0;
frac_lsb = DECOMPOSED_IMPLICIT_BIT >> (a->exp & 63);
frac_lsb = DECOMPOSED_IMPLICIT_BIT >> (MIN(a->exp, frac_size) & 63);
}
frac_lsbm1 = frac_lsb >> 1;