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/*
* Copyright 2017 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.
*/
#ifndef wasm_ast_bits_h
#define wasm_ast_bits_h
#include "support/bits.h"
namespace wasm {
struct Bits {
// get a mask to keep only the low # of bits
static int32_t lowBitMask(int32_t bits) {
uint32_t ret = -1;
if (bits >= 32) return ret;
return ret >> (32 - bits);
}
// checks if the input is a mask of lower bits, i.e., all 1s up to some high bit, and all zeros
// from there. returns the number of masked bits, or 0 if this is not such a mask
static uint32_t getMaskedBits(uint32_t mask) {
if (mask == uint32_t(-1)) return 32; // all the bits
if (mask == 0) return 0; // trivially not a mask
// otherwise, see if adding one turns this into a 1-bit thing, 00011111 + 1 => 00100000
if (PopCount(mask + 1) != 1) return 0;
// this is indeed a mask
return 32 - CountLeadingZeroes(mask);
}
// gets the number of effective shifts a shift operation does. In
// wasm, only 5 bits matter for 32-bit shifts, and 6 for 64.
static Index getEffectiveShifts(Index amount, WasmType type) {
if (type == i32) {
return amount & 31;
} else if (type == i64) {
return amount & 63;
}
WASM_UNREACHABLE();
}
static Index getEffectiveShifts(Const* amount) {
if (amount->type == i32) {
return getEffectiveShifts(amount->value.geti32(), i32);
} else if (amount->type == i64) {
return getEffectiveShifts(amount->value.geti64(), i64);
}
WASM_UNREACHABLE();
}
};
} // namespace wasm
#endif // wasm_ast_bits_h
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