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https://github.com/jart/cosmopolitan.git
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7e0a09feec
This change ports APE Loader to Linux AARCH64, so that Raspberry Pi users can run programs like redbean, without the executable needing to modify itself. Progress has also slipped into this change on the issue of making progress better conforming to user expectations and industry standards regarding which symbols we're allowed to declare
60 lines
1.8 KiB
C
60 lines
1.8 KiB
C
/* clang-format off */
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/* ===-- ctzsi2.c - Implement __ctzsi2 -------------------------------------===
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*
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* The LLVM Compiler Infrastructure
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*
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* This file is dual licensed under the MIT and the University of Illinois Open
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* Source Licenses. See LICENSE.TXT for details.
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*
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* ===----------------------------------------------------------------------===
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*
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* This file implements __ctzsi2 for the compiler_rt library.
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*
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* ===----------------------------------------------------------------------===
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*/
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__static_yoink("huge_compiler_rt_license");
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#include "third_party/compiler_rt/int_lib.h"
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/* Returns: the number of trailing 0-bits */
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/* Precondition: a != 0 */
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COMPILER_RT_ABI si_int
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__ctzsi2(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 & 0x0000FFFF) == 0) << 4; /* if (x has no small bits) t = 16 else 0 */
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x >>= t; /* x = [0 - 0xFFFF] + higher garbage bits */
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su_int r = t; /* r = [0, 16] */
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/* return r + ctz(x) */
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t = ((x & 0x00FF) == 0) << 3;
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x >>= t; /* x = [0 - 0xFF] + higher garbage bits */
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r += t; /* r = [0, 8, 16, 24] */
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/* return r + ctz(x) */
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t = ((x & 0x0F) == 0) << 2;
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x >>= t; /* x = [0 - 0xF] + higher garbage bits */
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r += t; /* r = [0, 4, 8, 12, 16, 20, 24, 28] */
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/* return r + ctz(x) */
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t = ((x & 0x3) == 0) << 1;
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x >>= t;
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x &= 3; /* x = [0 - 3] */
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r += t; /* r = [0 - 30] and is even */
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/* return r + ctz(x) */
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/* The branch-less return statement below is equivalent
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* to the following switch statement:
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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 2:
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* return r + 1;
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* case 1:
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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 >> 1)) & -((x & 1) == 0));
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}
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