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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.
*/
#define wasm_support_bits_definitions
#include "support/bits.h"
#include "../compiler-support.h"
#include "support/utilities.h"
namespace wasm {
template<> int PopCount<uint8_t>(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];
}
template<> int PopCount<uint16_t>(uint16_t v) {
return PopCount((uint8_t)(v & 0xff)) + PopCount((uint8_t)(v >> 8));
}
template<> int PopCount<uint32_t>(uint32_t v) {
// 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;
}
template<> int PopCount<uint64_t>(uint64_t v) {
return PopCount((uint32_t)v) + PopCount((uint32_t)(v >> 32));
}
template<> uint32_t BitReverse<uint32_t>(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;
}
template<> int CountTrailingZeroes<uint32_t>(uint32_t v) {
// 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 v ? (int)tbl[((uint32_t)((v & -v) * 0x077CB531U)) >> 27] : 32;
}
template<> int CountTrailingZeroes<uint64_t>(uint64_t v) {
return (uint32_t)v ? CountTrailingZeroes((uint32_t)v)
: 32 + CountTrailingZeroes((uint32_t)(v >> 32));
}
template<> int CountLeadingZeroes<uint32_t>(uint32_t v) {
// 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 v ? (int)tbl[((uint32_t)(v * 0x07C4ACDDU)) >> 27] : 32;
}
template<> int CountLeadingZeroes<uint64_t>(uint64_t v) {
return v >> 32 ? CountLeadingZeroes((uint32_t)(v >> 32))
: 32 + CountLeadingZeroes((uint32_t)v);
}
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) {
switch (v) {
case 0:
return 1;
case 1:
return 2;
case 2:
return 4;
case 3:
return 8;
case 4:
return 16;
case 5:
return 32;
default:
return 1 << v;
}
}
} // namespace wasm
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