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-id = 2817
-title = "Strange floating-point behaviour under Windows with some CPU models"
-state = "opened"
-created_at = "2025-02-18T12:02:17.591Z"
-closed_at = "n/a"
-labels = ["Softfloat", "target: i386"]
-url = "https://gitlab.com/qemu-project/qemu/-/issues/2817"
-host-os = "Debian 12"
-host-arch = "x86_64"
-qemu-version = "QEMU emulator version 7.2.13 (Debian 1:7.2+dfsg-7+deb12u7)"
-guest-os = "Windows 10, Windows Server 2022"
-guest-arch = "x86_64"
-description = """I'm encountering a very weird bug with some floating-point maths code, but only under very specific configurations. First I thought it was a Clang bug, but then further digging eventually showed it to only occur under Windows VMs with specific QEMU CPU options, I'm not certain whether it is a QEMU/KVM bug or a Windows bug, but thought starting here would be easiest.
-
-When compiled under MSVC Clang with modern CPU instructions disabled (e.g. `-march=pentium3` or `-march=pentium-mmx`), the `floorf()` call in the following program always returns 0.0, while the truncation works correctly:
-
-```
-#include <math.h>
-#include <stdio.h>
-#include <stdlib.h>
-
-int main(int argc, char **argv)
-{
-\tfloat n = atof(argv[1]);
-\tprintf("n = %f\\n", n);
-\t
-\tfloat f = floorf(n);
-\tprintf("f = %f\\n", f);
-\t
-\tfloat c = (int)(n);
-\tprintf("c = %f\\n", c);
-\t
-\treturn 0;
-}
-```
-
-Example output on an affected VM:
-
-```
-C:\\Users\\Administrator> floorf-p3.exe 10
-n = 10.000000
-f = 0.000000
-c = 10.000000
-
-C:\\Users\\Administrator> floorf-p4.exe 10
-n = 10.000000
-f = 10.000000
-c = 10.000000
-```
-
-(`floorf-p3.exe` was compiled with `-march=pentium3` and `floorf-p4.exe` with `-march=pentium4` above)
-
-I've tried a few QEMU CPU models on a variety of Intel/AMD VM hosts and two different Windows versions (10 and Server 2022), and observed the following:
-
-* `host-passthrough` - works (on AMD and Intel hosts)
-* `qemu64` - broken
-* `EPYC-Milan` - works
-* `Westmere` - works
-* `Penryn` - broken
-
-(I also reported this via the mailing list, but I think it might've swallowed my post)"""
-reproduce = "n/a"
-additional = "n/a"