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%include "defs.asm"
;************************* substring64.asm **********************************
; Author: Agner Fog
; Date created: 2011-07-18
; Last modified: 2011-07-18
; Source URL: www.agner.org/optimize
; Project: asmlib.zip
; Description:
; Makes a substring of a zero-terminated ASCII string
;
; C++ prototype:
; extern "C"
; size_t A_substring(char * dest, const char * source, size_t pos, size_t len);
; Makes a substring from source, starting at position pos (zero-based) and length
; len and stores it in the array dest. It is the responsibility of the programmer
; that the size of the dest array is at least len + 1.
; The return value is the actual length of the substring. This may be less than
; len if the length of source is less than pos + len.
;
; Copyright (c) 2011 GNU General Public License www.gnu.org/licenses/gpl.html
;******************************************************************************
global A_substring: function ; Function _A_substring
extern A_strlen
extern A_memcpy
SECTION .text
; extern "C"
; size_t A_substring(char * dest, const char * source, size_t pos, size_t len);
%ifdef WINDOWS
%define par1 rcx ; dest
%define par2 rdx ; source
%define par3 r8 ; pos
%define par4 r9 ; len
%else ; UNIX
%define par1 rdi
%define par2 rsi
%define par3 rdx
%define par4 rcx
%endif
A_substring:
push par1
push par2
push par3
push par4
mov par1, par2
call A_strlen ; rax = strlen(source)
pop par4
pop par3
pop par2
pop par1
sub rax, par3 ; max length = strlen(source) - pos
jbe empty ; strlen(source) <= pos. Return empty string
cmp rax, par4
cmova rax, par4 ; min(len, maxlen)
add par2, par3 ; source + pos = source for memcpy
mov par3, rax ; length for memcpy
push rax ; new length
call A_memcpy
pop rcx ; new length = return value, rax = dest
mov byte [rcx+rax], 0 ; terminating zero
mov rax, rcx ; return new length
ret
empty: ; return empty string
xor eax, eax ; return 0
mov byte [par1], al
ret
;A_substring END
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