| // run |
| |
| // Copyright 2026 The Go Authors. All rights reserved. |
| // Use of this source code is governed by a BSD-style |
| // license that can be found in the LICENSE file. |
| |
| // Folding a paired modulo-count shift into a double-register shift |
| // (SHRD/SHLD on amd64) must not drop the second operand when the |
| // shift count is zero modulo 64. |
| |
| package main |
| |
| //go:noinline |
| func shrd(lo, hi uint64, bits uint) uint64 { |
| return lo>>(bits&63) | hi<<((-bits)&63) |
| } |
| |
| func main() { |
| got := shrd(0x1111000000000000, 0x2222, 0) |
| want := uint64(0x1111000000002222) |
| if got != want { |
| println("shrd zero count: got", got, "want", want) |
| panic("FAIL") |
| } |
| } |
