2020-06-16 13:38:43 +00:00
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/*-*- mode:unix-assembly; indent-tabs-mode:t; tab-width:8; coding:utf-8 -*-│
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2020-06-15 14:18:57 +00:00
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│vi: set et ft=asm ts=8 sw=8 fenc=utf-8 :vi│
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╞══════════════════════════════════════════════════════════════════════════════╡
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│ Copyright 2020 Justine Alexandra Roberts Tunney │
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│ │
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2020-12-28 01:18:44 +00:00
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│ Permission to use, copy, modify, and/or distribute this software for │
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│ any purpose with or without fee is hereby granted, provided that the │
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│ above copyright notice and this permission notice appear in all copies. │
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2020-06-15 14:18:57 +00:00
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│ │
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2020-12-28 01:18:44 +00:00
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│ THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL │
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│ WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED │
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│ WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE │
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│ AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL │
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│ DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR │
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│ PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER │
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│ TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR │
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│ PERFORMANCE OF THIS SOFTWARE. │
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2020-06-15 14:18:57 +00:00
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╚─────────────────────────────────────────────────────────────────────────────*/
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2021-03-01 07:42:35 +00:00
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#include "libc/macros.internal.h"
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2020-06-15 14:18:57 +00:00
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2021-02-08 17:19:00 +00:00
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// Fast log₁₀ when 𝑥 is an integer.
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//
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// @param rdi is uint64 𝑥
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// @domain 0<𝑥<2⁶⁴ ∧ 𝑥∊ℤ
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2020-06-15 14:18:57 +00:00
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llog10: .leafprologue
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.profilable
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bsr %rdi,%rax
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jz 3f
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lea llog10data(%rip),%rdx
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movsbl 1(%rdx,%rax),%eax
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cmp 2f-1f(%rdx,%rax,8),%rdi
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sbb $0,%al
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jmp 4f
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3: xor %eax,%eax # domain error
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4: .leafepilogue
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.endfn llog10,globl
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.rodata
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llog10data:
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1: .byte 0, 0, 0, 0, 1, 1, 1, 2, 2, 2, 3, 3, 3, 3, 4, 4
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.byte 4, 5, 5, 5, 6, 6, 6, 6, 7, 7, 7, 8, 8, 8, 9, 9
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.byte 9, 9,10,10,10,11,11,11,12,12,12,12,13,13,13,14
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.byte 14,14,15,15,15,15,16,16,16,17,17,17,18,18,18,18
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.byte 19,19,19
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.align 8
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2: .quad 0
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.quad 10
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.quad 100
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.quad 1000
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.quad 10000
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.quad 100000
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.quad 1000000
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.quad 10000000
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.quad 100000000
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.quad 1000000000
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.quad 10000000000
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.quad 100000000000
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.quad 1000000000000
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.quad 10000000000000
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.quad 100000000000000
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.quad 1000000000000000
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.quad 10000000000000000
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.quad 100000000000000000
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.endobj llog10data
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.previous
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2020-06-16 02:01:28 +00:00
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.source __FILE__
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