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/*
* Copyright 2015 WebAssembly Community Group participants
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
#include "support/bits.h"
#include "../compiler-support.h"
#include "support/utilities.h"
#ifdef _MSC_VER
#include <intrin.h>
#endif
namespace wasm {
namespace Bits {
int popCount(uint8_t v) {
// Small table lookup.
static const uint8_t tbl[32] = {0, 1, 1, 2, 1, 2, 2, 3, 1, 2, 2,
3, 2, 3, 3, 4, 1, 2, 2, 3, 2, 3,
3, 4, 2, 3, 3, 4, 3, 4, 4, 5};
return tbl[v & 0xf] + tbl[v >> 4];
}
int popCount(uint16_t v) {
#if __has_builtin(__builtin_popcount) || defined(__GNUC__)
return __builtin_popcount(v);
#else
return popCount((uint8_t)(v & 0xFF)) + popCount((uint8_t)(v >> 8));
#endif
}
int popCount(uint32_t v) {
#if __has_builtin(__builtin_popcount) || defined(__GNUC__)
return __builtin_popcount(v);
#else
// See Stanford bithacks, counting bits set in parallel, "best method":
// http://graphics.stanford.edu/~seander/bithacks.html#CountBitsSetParallel
v = v - ((v >> 1) & 0x55555555);
v = (v & 0x33333333) + ((v >> 2) & 0x33333333);
return (((v + (v >> 4)) & 0xF0F0F0F) * 0x1010101) >> 24;
#endif
}
int popCount(uint64_t v) {
#if __has_builtin(__builtin_popcount) || defined(__GNUC__)
return __builtin_popcountll(v);
#else
return popCount((uint32_t)v) + popCount((uint32_t)(v >> 32));
#endif
}
uint32_t bitReverse(uint32_t v) {
// See Hacker's Delight, first edition, figure 7-1.
v = ((v & 0x55555555) << 1) | ((v >> 1) & 0x55555555);
v = ((v & 0x33333333) << 2) | ((v >> 2) & 0x33333333);
v = ((v & 0x0F0F0F0F) << 4) | ((v >> 4) & 0x0F0F0F0F);
v = (v << 24) | ((v & 0xFF00) << 8) | ((v >> 8) & 0xFF00) | (v >> 24);
return v;
}
int countTrailingZeroes(uint32_t v) {
if (v == 0) {
return 32;
}
#if __has_builtin(__builtin_ctz) || defined(__GNUC__)
return __builtin_ctz(v);
#elif defined(_MSC_VER)
unsigned long count;
_BitScanForward(&count, v);
return (int)count;
#else
// See Stanford bithacks, count the consecutive zero bits (trailing) on the
// right with multiply and lookup:
// http://graphics.stanford.edu/~seander/bithacks.html#ZerosOnRightMultLookup
static const uint8_t tbl[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 (int)tbl[((uint32_t)((v & -v) * 0x077CB531U)) >> 27];
#endif
}
int countTrailingZeroes(uint64_t v) {
if (v == 0) {
return 64;
}
#if __has_builtin(__builtin_ctzll) || defined(__GNUC__)
return __builtin_ctzll(v);
#elif defined(_MSC_VER) && defined(_M_X64)
unsigned long count;
_BitScanForward64(&count, v);
return (int)count;
#else
return (uint32_t)v ? countTrailingZeroes((uint32_t)v)
: 32 + countTrailingZeroes((uint32_t)(v >> 32));
#endif
}
int countLeadingZeroes(uint32_t v) {
if (v == 0) {
return 32;
}
#if __has_builtin(__builtin_clz) || defined(__GNUC__)
return __builtin_clz(v);
#elif defined(_MSC_VER)
unsigned long count;
_BitScanReverse(&count, v);
// BitScanReverse gives the bit position (0 for the LSB, then 1, etc.) of the
// first bit that is 1, when looking from the MSB. To count leading zeros, we
// need to adjust that.
return 31 - int(count);
#else
// See Stanford bithacks, find the log base 2 of an N-bit integer in
// O(lg(N)) operations with multiply and lookup:
// http://graphics.stanford.edu/~seander/bithacks.html#IntegerLogDeBruijn
static const uint8_t tbl[32] = {31, 22, 30, 21, 18, 10, 29, 2, 20, 17, 15,
13, 9, 6, 28, 1, 23, 19, 11, 3, 16, 14,
7, 24, 12, 4, 8, 25, 5, 26, 27, 0};
v = v | (v >> 1);
v = v | (v >> 2);
v = v | (v >> 4);
v = v | (v >> 8);
v = v | (v >> 16);
return (int)tbl[((uint32_t)(v * 0x07C4ACDDU)) >> 27];
#endif
}
int countLeadingZeroes(uint64_t v) {
if (v == 0) {
return 64;
}
#if __has_builtin(__builtin_clzll) || defined(__GNUC__)
return __builtin_clzll(v);
#elif defined(_MSC_VER) && defined(_M_X64)
unsigned long count;
_BitScanReverse64(&count, v);
return 63 - int(count);
#else
return v >> 32 ? countLeadingZeroes((uint32_t)(v >> 32))
: 32 + countLeadingZeroes((uint32_t)v);
#endif
}
int ceilLog2(uint32_t v) { return 32 - countLeadingZeroes(v - 1); }
int ceilLog2(uint64_t v) { return 64 - countLeadingZeroes(v - 1); }
uint32_t log2(uint32_t v) {
switch (v) {
default:
WASM_UNREACHABLE("invalid value");
case 1:
return 0;
case 2:
return 1;
case 4:
return 2;
case 8:
return 3;
case 16:
return 4;
case 32:
return 5;
}
}
uint32_t pow2(uint32_t v) { return 1 << v; }
} // namespace Bits
} // namespace wasm
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