// Copyright 2009 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.package subtleimport ()// ConstantTimeCompare returns 1 if the two slices, x and y, have equal contents// and 0 otherwise. The time taken is a function of the length of the slices and// is independent of the contents. If the lengths of x and y do not match it// returns 0 immediately.func (, []byte) int {iflen() != len() {return0 }varbytefor := 0; < len(); ++ { |= [] ^ [] }returnConstantTimeByteEq(, 0)}// ConstantTimeLessOrEqBytes returns 1 if x <= y and 0 otherwise. The comparison// is lexigraphical, or big-endian. The time taken is a function of the length of// the slices and is independent of the contents. If the lengths of x and y do not// match it returns 0 immediately.func (, []byte) int {iflen() != len() {return0 }// Do a constant time subtraction chain y - x. // If there is no borrow at the end, then x <= y.varuint64forlen() > 8 { := byteorder.BEUint64([len()-8:]) := byteorder.BEUint64([len()-8:]) _, = bits.Sub64(, , ) = [:len()-8] = [:len()-8] }iflen() > 0 { := make([]byte, 8) := make([]byte, 8)copy([8-len():], )copy([8-len():], ) := byteorder.BEUint64() := byteorder.BEUint64() _, = bits.Sub64(, , ) }returnint( ^ 1)}// ConstantTimeSelect returns x if v == 1 and y if v == 0.// Its behavior is undefined if v takes any other value.func (, , int) int { return ^(-1)& | (-1)& }// ConstantTimeByteEq returns 1 if x == y and 0 otherwise.func (, uint8) int {returnint((uint32(^) - 1) >> 31)}// ConstantTimeEq returns 1 if x == y and 0 otherwise.func (, int32) int {returnint((uint64(uint32(^)) - 1) >> 63)}// ConstantTimeCopy copies the contents of y into x (a slice of equal length)// if v == 1. If v == 0, x is left unchanged. Its behavior is undefined if v// takes any other value.func ( int, , []byte) {iflen() != len() {panic("subtle: slices have different lengths") } := byte( - 1) := byte(^( - 1))for := 0; < len(); ++ { [] = []& | []& }}// ConstantTimeLessOrEq returns 1 if x <= y and 0 otherwise.// Its behavior is undefined if x or y are negative or > 2**31 - 1.func (, int) int { := int32() := int32()returnint((( - - 1) >> 31) & 1)}
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