gistfile1.h

#include "stdafx.h"
#include <stdlib.h>

/* Magic numbers for the algorithm */
static const unsigned long mask01 = 0x01010101;
static const unsigned long mask80 = 0x80808080;

#define	LONGPTR_MASK (sizeof(long) - 1)

/*
 * Helper macro to return string length if we caught the zero
 * byte.
 */
#define testbyte(x)				\
	do {					\
		if (p[x] == '\0')		\
		    return (p - str + x);	\
	} while (0)

inline size_t
strlen2(const char *str)
{
	const char *p;
	const unsigned long *lp;

	/* Skip the first few bytes until we have an aligned p */
	for (p = str; (uintptr_t)p & LONGPTR_MASK; p++)
	    if (*p == '\0')
		return (p - str);

	/* Scan the rest of the string using word sized operation */
	for (lp = (const unsigned long *)p; ; lp++)
	    if ((*lp - mask01) & mask80) {
		p = (const char *)(lp);
		testbyte(0);
		testbyte(1);
		testbyte(2);
		testbyte(3);
	    }

	/* NOTREACHED */
	return 0;
}

inline int strlen3(const char* string)
{
	__asm
	{
		mov     ecx, string              ; ecx -> string
		test    ecx,3                   ; test if string is aligned on 32 bits
		je      short main_loop

str_misaligned:
		; simple byte loop until string is aligned
		mov     al,byte ptr [ecx]
		add     ecx,1
		test    al,al
		je      short byte_3
		test    ecx,3
		jne     short str_misaligned
		add     eax,dword ptr 0         ; 5 byte nop to align label below
		align   16                      ; should be redundant

main_loop:
		mov     eax,dword ptr [ecx]     ; read 4 bytes
		mov     edx,7efefeffh
		add     edx,eax
		xor     eax,-1
		xor     eax,edx
		add     ecx,4
		test    eax,81010100h
		je      short main_loop
		; found zero byte in the loop
		mov     eax,[ecx - 4]
		test    al,al                   ; is it byte 0
		je      short byte_0
		test    ah,ah                   ; is it byte 1
		je      short byte_1
		test    eax,00ff0000h           ; is it byte 2
		je      short byte_2
		test    eax,0ff000000h          ; is it byte 3
		je      short byte_3
		jmp     short main_loop         ; taken if bits 24-30 are clear and bit
		; 31 is set

byte_3:
		lea     eax,[ecx - 1]
		mov     ecx,string
		sub     eax,ecx
		jmp ReturnLabel
byte_2:
		lea     eax,[ecx - 2]
		mov     ecx,string
		sub     eax,ecx
		jmp ReturnLabel
byte_1:
		lea     eax,[ecx - 3]
		mov     ecx,string
		sub     eax,ecx
		jmp ReturnLabel
byte_0:
		lea     eax,[ecx - 4]
		mov     ecx,string
		sub     eax,ecx
		jmp ReturnLabel
	}

ReturnLabel:
	return;
}

#include "logger.h"
int _tmain(int argc, _TCHAR* argv[])
{
	char* str = "aaabcaaaaaaaaaaaaaaaaaaaaaabbbbbbbbbdefffffghgfgfgfgfggaaaaaaaaaaaaffffff" \
		"aaabcaaaaaaaaaaaaaaaaaaaaaabbbbbbbbbdefffffghgfgfgfgfggaaaaaaaaaaaaffffff" \
		"fffgggggggggggggghhhhhhhhhhhhhhhhhhhhhhhhhhhhheeeeeeeeeeeeeeeeeeeeghhhhhhhhhhhhhh";

	CPerfTimer timer1(TRUE);
	for (int i=0; i< 100000; i++)
	{
		int len = strlen2(str);
	}
	timer1.Stop();
	double timeA = timer1.Elapsedus();

	timer1.Start(TRUE);
	for (int i=0; i< 100000; i++)
	{
		int len = strlen(str);
	}
	timer1.Stop();
	double timeB = timer1.Elapsedus();

	timer1.Start(TRUE);
	for (int i=0; i< 100000; i++)
	{
		int len = strlen3(str);
	}
	timer1.Stop();
	double timeC = timer1.Elapsedus();

	return 0;
}