common/math: use math/bits intrinsics for Safe* (#21316)

This is a resubmit of ledgerwatch/turbo-geth#556. The performance
benefit of this change is negligible, but it does remove a TODO.
This commit is contained in:
Felix Lange 2020-07-09 17:45:49 +02:00 committed by GitHub
parent bcb3087450
commit 6ccce0906a
No known key found for this signature in database
GPG Key ID: 4AEE18F83AFDEB23

View File

@ -18,6 +18,7 @@ package math
import (
"fmt"
"math/bits"
"strconv"
)
@ -78,22 +79,20 @@ func MustParseUint64(s string) uint64 {
return v
}
// NOTE: The following methods need to be optimised using either bit checking or asm
// SafeSub returns subtraction result and whether overflow occurred.
// SafeSub returns x-y and checks for overflow.
func SafeSub(x, y uint64) (uint64, bool) {
return x - y, x < y
diff, borrowOut := bits.Sub64(x, y, 0)
return diff, borrowOut != 0
}
// SafeAdd returns the result and whether overflow occurred.
// SafeAdd returns x+y and checks for overflow.
func SafeAdd(x, y uint64) (uint64, bool) {
return x + y, y > MaxUint64-x
sum, carryOut := bits.Add64(x, y, 0)
return sum, carryOut != 0
}
// SafeMul returns multiplication result and whether overflow occurred.
// SafeMul returns x*y and checks for overflow.
func SafeMul(x, y uint64) (uint64, bool) {
if x == 0 || y == 0 {
return 0, false
}
return x * y, y > MaxUint64/x
hi, lo := bits.Mul64(x, y)
return lo, hi != 0
}