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runtime/internal/math: add Add64

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This makes the intrinsic available on 64-bit platforms,
since the runtime cannot import math/bits.

Change-Id: I5296cc6a97d1cb4756ab369d96dc9605df9f8247
Reviewed-on: https://go-review.googlesource.com/c/go/+/516861
Reviewed-by: Keith Randall <khr@google.com>
Run-TryBot: Russ Cox <rsc@golang.org>
Reviewed-by: Keith Randall <khr@golang.org>
Auto-Submit: Russ Cox <rsc@golang.org>
TryBot-Bypass: Russ Cox <rsc@golang.org>
This commit is contained in:
Russ Cox 2023-08-07 15:52:18 -04:00 committed by Gopher Robot
parent 98c9f271d6
commit 53895bf993
2 changed files with 16 additions and 0 deletions
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1
src/cmd/compile/internal/ssagen/ssa.go
View File

@ -4870,6 +4870,7 @@ func InitTables() {
},
sys.AMD64, sys.ARM64, sys.PPC64, sys.S390X, sys.RISCV64, sys.Loong64, sys.MIPS64)
alias("math/bits", "Add", "math/bits", "Add64", p8...)
alias("runtime/internal/math", "Add64", "math/bits", "Add64", all...)
addF("math/bits", "Sub64",
func(s *state, n *ir.CallExpr, args []*ssa.Value) *ssa.Value {
return s.newValue3(ssa.OpSub64borrow, types.NewTuple(types.Types[types.TUINT64], types.Types[types.TUINT64]), args[0], args[1], args[2])

15
src/runtime/internal/math/math.go
View File

@ -38,3 +38,18 @@ func Mul64(x, y uint64) (hi, lo uint64) {
lo = x * y
return
}
// Add64 returns the sum with carry of x, y and carry: sum = x + y + carry.
// The carry input must be 0 or 1; otherwise the behavior is undefined.
// The carryOut output is guaranteed to be 0 or 1.
//
// This function's execution time does not depend on the inputs.
// On supported platforms this is an intrinsic lowered by the compiler.
func Add64(x, y, carry uint64) (sum, carryOut uint64) {
sum = x + y + carry
// The sum will overflow if both top bits are set (x & y) or if one of them
// is (x | y), and a carry from the lower place happened. If such a carry
// happens, the top bit will be 1 + 0 + 1 = 0 (&^ sum).
carryOut = ((x & y) | ((x | y) &^ sum)) >> 63
return
}