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54 lines
1.5 KiB
C
54 lines
1.5 KiB
C
/* ===-- clzsi2.c - Implement __clzsi2 -------------------------------------===
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*
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* The LLVM Compiler Infrastructure
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*
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* This file is distributed under the University of Illinois Open Source
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* License. See LICENSE.TXT for details.
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*
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* ===----------------------------------------------------------------------===
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*
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* This file implements __clzsi2 for the compiler_rt library.
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*
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* ===----------------------------------------------------------------------===
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*/
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#include "int_lib.h"
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/* Returns: the number of leading 0-bits */
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/* Precondition: a != 0 */
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si_int
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__clzsi2(si_int a)
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{
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su_int x = (su_int)a;
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si_int t = ((x & 0xFFFF0000) == 0) << 4; /* if (x is small) t = 16 else 0 */
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x >>= 16 - t; /* x = [0 - 0xFFFF] */
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su_int r = t; /* r = [0, 16] */
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/* return r + clz(x) */
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t = ((x & 0xFF00) == 0) << 3;
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x >>= 8 - t; /* x = [0 - 0xFF] */
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r += t; /* r = [0, 8, 16, 24] */
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/* return r + clz(x) */
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t = ((x & 0xF0) == 0) << 2;
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x >>= 4 - t; /* x = [0 - 0xF] */
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r += t; /* r = [0, 4, 8, 12, 16, 20, 24, 28] */
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/* return r + clz(x) */
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t = ((x & 0xC) == 0) << 1;
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x >>= 2 - t; /* x = [0 - 3] */
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r += t; /* r = [0 - 30] and is even */
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/* return r + clz(x) */
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/* switch (x)
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* {
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* case 0:
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* return r + 2;
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* case 1:
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* return r + 1;
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* case 2:
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* case 3:
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* return r;
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* }
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*/
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return r + ((2 - x) & -((x & 2) == 0));
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}
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