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43 lines
1.4 KiB
C
43 lines
1.4 KiB
C
/*
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* Copyright 2024 Google LLC
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*
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* Licensed under the Apache License, Version 2.0 (the "License");
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* you may not use this file except in compliance with the License.
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* You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS,
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* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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* See the License for the specific language governing permissions and
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* limitations under the License.
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*/
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#include "util/attributes.h"
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#include <stdint.h>
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// Override libgcc's table-driven __builtin_popcount implementation
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#ifdef __arm__
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EXTERNALLY_VISIBLE int __popcountsi2(uint32_t val) {
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// Adapted from http://www.sciencezero.org/index.php?title=ARM%3a_Count_ones_%28bit_count%29
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uint32_t tmp;
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__asm("and %[tmp], %[val], #0xaaaaaaaa\n\t"
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"sub %[val], %[val], %[tmp], lsr #1\n\t"
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"and %[tmp], %[val], #0xcccccccc\n\t"
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"and %[val], %[val], #0x33333333\n\t"
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"add %[val], %[val], %[tmp], lsr #2\n\t"
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"add %[val], %[val], %[val], lsr #4\n\t"
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"and %[val], %[val], #0x0f0f0f0f\n\t"
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"add %[val], %[val], %[val], lsr #8\n\t"
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"add %[val], %[val], %[val], lsr #16\n\t"
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"and %[val], %[val], #63\n\t"
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: [val] "+l" (val), [tmp] "=&l" (tmp));
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return val;
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}
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#endif // __arm__
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