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135 lines
2.6 KiB
ArmAsm
135 lines
2.6 KiB
ArmAsm
#include <asm.inc>
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#include <ksamd64.inc>
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.code64
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#if 0
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page ,132
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title strlen - return the length of a null-terminated string
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;***
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;strlen.asm - contains strlen() routine
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;
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; Copyright (c) Microsoft Corporation. All rights reserved.
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;
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;Purpose:
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; strlen returns the length of a null-terminated string,
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; not including the null byte itself.
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;
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;*******************************************************************************
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include ksamd64.inc
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subttl "strlen"
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;***
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;strlen - return the length of a null-terminated string
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;
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;Purpose:
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; Finds the length in bytes of the given string, not including
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; the final null character.
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;
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; Algorithm:
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; int strlen (const char * str)
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; {
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; int length = 0;
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;
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; while( *str++ )
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; ++length;
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;
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; return( length );
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; }
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;
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;Entry:
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; const char * str - string whose length is to be computed
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;
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;Exit:
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; EAX = length of the string "str", exclusive of the final null byte
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;
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;Uses:
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; EAX, ECX, EDX
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;
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;Exceptions:
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;
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;*******************************************************************************
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#endif
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LEAF_ENTRY_ARG1 strlen, _TEXT, buf:ptr byte
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//OPTION PROLOGUE:NONE, EPILOGUE:NONE
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mov rax, rcx
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neg rcx // for later
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test rax, 7
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jz main_loop_entry
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.byte HEX(66), HEX(90)
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byte_loop_begin:
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mov dl, [rax]
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inc rax
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test dl, dl
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jz return_byte_7
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test al, 7
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jnz byte_loop_begin
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main_loop_entry:
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mov r8, HEX(7efefefefefefeff)
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mov r11, HEX(8101010101010100)
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main_loop_begin:
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mov rdx, [rax]
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mov r9, r8
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add rax, 8
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add r9, rdx
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not rdx
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xor rdx, r9
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and rdx, r11
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je main_loop_begin
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main_loop_end:
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mov rdx, [rax-8]
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test dl, dl
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jz return_byte_0
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test dh, dh
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jz return_byte_1
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shr rdx, 16
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test dl, dl
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jz return_byte_2
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test dh, dh
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jz return_byte_3
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shr rdx, 16
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test dl, dl
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jz return_byte_4
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test dh, dh
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jz return_byte_5
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shr edx, 16
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test dl, dl
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jz return_byte_6
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test dh, dh
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jnz main_loop_begin
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return_byte_7:
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lea rax, [rax+rcx-1]
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ret
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return_byte_6:
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lea rax, [rax+rcx-2]
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ret
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return_byte_5:
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lea rax, [rax+rcx-3]
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ret
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return_byte_4:
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lea rax, [rax+rcx-4]
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ret
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return_byte_3:
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lea rax, [rax+rcx-5]
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ret
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return_byte_2:
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lea rax, [rax+rcx-6]
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ret
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return_byte_1:
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lea rax, [rax+rcx-7]
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ret
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return_byte_0:
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lea rax, [rax+rcx-8]
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ret
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LEAF_END strlen, _TEXT
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end
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