Repository navigation
CopySign is slow #77579
Description
Description
[MethodImpl(MethodImplOptions.AggressiveInlining)]
public static int CopySign_A1(int value, int sign) {
return int.CopySign(value, sign);
}
[MethodImpl(MethodImplOptions.AggressiveInlining)]
public static int SignZeroToOne(Int32 value) {
return (value >> (32 - 1)) - (~value >> (32 - 1));
}
[MethodImpl(MethodImplOptions.AggressiveInlining | MethodImplOptions.AggressiveOptimization)]
public static int CopySign_A2(int value, int sign) {
if (int.MinValue != value || 0 > sign) {
return value * SignZeroToOne(value ^ sign);
}
return checked(-value);
}CopySign_A2 is mush faster than CopySign_A1.
Configuration
.NET 7 RC
Data
Random inputs (x10000)
X64 RyuJIT AVX2 (Coffee Lake)
| Method | Mean | Error | StdDev |
|---|---|---|---|
| Test_0 | 3.093 us | 0.0064 us | 0.0060 us |
| Test_CopySign_A1 | 25.423 us | 0.4784 us | 0.4475 us |
| Test_CopySign_A2 | 6.486 us | 0.1288 us | 0.1323 us |
Test_0: nop
Activity
EgorBo commentedon Oct 28, 2022
@LEI-Hongfaan do you want to contribute that to
CopySignimpl?Although, this API doesn't look popular: https://grep.app/search?q=.CopySign%28&words=true&filter[lang][0]=C%23
EgorBo commentedon Oct 28, 2022
Removing codegen label as it's unlikely we want/need to teach jit to recognize such idioms
Fix dotnet#77579
Improve integer CopySign with branchless bit-twiddling (#130563)
Improve integer CopySign with branchless bit-twiddling (#130563)