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/* Copyright 2017 The ChromiumOS Authors
* Use of this source code is governed by a BSD-style license that can be
* found in the LICENSE file.
*
* Software emulation for CTZ instruction
*/
#include "common.h"
/**
* Count trailing zeros
*
* @param x non null integer.
* @return the number of trailing 0-bits in x,
* starting at the least significant bit position.
*
* Using a de Brujin sequence, as documented here:
* http://graphics.stanford.edu/~seander/bithacks.html#ZerosOnRightMultLookup
*/
int __keep __ctzsi2(int x)
{
static const uint8_t MulDeBruijnBitPos[32] = {
0, 1, 28, 2, 29, 14, 24, 3, 30, 22, 20, 15, 25, 17, 4, 8,
31, 27, 13, 23, 21, 19, 16, 7, 26, 12, 18, 6, 11, 5, 10, 9
};
return MulDeBruijnBitPos[((uint32_t)((x & -x) * 0x077CB531U)) >> 27];
}
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