https://bugs.freebsd.org/bugzilla/show_bug.cgi?id=284905
Bug ID: 284905
Summary: __builtin_powf produces incorrect result on FreeBSD
Product: Base System
Version: CURRENT
Hardware: Any
OS: Any
Status: New
Severity: Affects Only Me
Priority: ---
Component: misc
Assignee: b...@freebsd.org
Reporter: y...@freebsd.org
Reposting from https://github.com/llvm/llvm-project/issues/127841:
Not sure if this is a clang bug or FreeBSD bug, but consider:
#include <cmath>
#include <iostream>
int main()
{
if (std::pow(10.0f, 11.0f) == __builtin_powf(10.0f, 11.0f))
std::cout << "Equals __builtin_powf\n";
else
std::cout << "Unequal to __builtin_powf\n";
if (std::pow(10.0f, 11.0f) == __builtin_powif(10.0f, 11))
std::cout << "Equals __builtin_powif\n";
else
std::cout << "Unequal to __builtin_powif\n";
std::cout << "32-bit float difference: " << (std::pow(10.0f, 11.0f) - 1e11f)
<< std::endl;
std::cout << "64-bit double difference: " << (std::pow(10.0f, 11.0f) - 1e11)
<< std::endl;
}
On my x86_64 FreeBSD VM, this gives:
builder@ganesha:~ $ uname -a
FreeBSD ganesha 14.2-RELEASE-p1 FreeBSD 14.2-RELEASE-p1 GENERIC amd64
builder@ganesha:~ $ clang++ --version
FreeBSD clang version 18.1.6 (https://github.com/llvm/llvm-project.git
llvmorg-18.1.6-0-g1118c2e05e67)
Target: x86_64-unknown-freebsd14.2
Thread model: posix
InstalledDir: /usr/bin
builder@ganesha:~ $ clang++ test.cxx
builder@ganesha:~ $ ./a.out
Equals __builtin_powf
Unequal to __builtin_powif
32-bit float difference: 8192
64-bit double difference: 6144
Whereas on macOS and OpenBSD (on the same hardware) it gives:
Equals __builtin_powf
Equals __builtin_powif
32-bit float difference: 0
64-bit double difference: -2048
Same result on x86_64 with clang 19.1 on godbolt:
https://godbolt.org/z/sceY9da3b
Only the FreeBSD case is different from everyone else.
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