OSDev.org

Code: Select all

il void SetMem(void* pMem, byte To, dword Size)
{
	if (Size < 128)
	{
		byte* p = (byte*)pMem;
		byte* pEnd = (byte*)pMem + Size;
			
		while (p < pEnd)
			*p++ = To;

		return;
	}

	byte* p = (byte*)pMem;
	byte* pEnd = (byte*)pMem + Size - sizeof(qword);

	qword Toqword = CharsToqword(To, To, To, To, To, To, To, To);

	// Align to qword boundary
	switch (((qword)pMem) & 0x7)
	{
		case 7:		*p++ = To;
		case 6:		*p++ = To;
		case 5:		*p++ = To;
		case 4:		*p++ = To;
		case 3:		*p++ = To;
		case 2:		*p++ = To;
		case 1:		*p++ = To;
	}

	while (p < pEnd)
	{
		*(qword*)p = Toqword;
		p += sizeof(qword);
	}

	pEnd += sizeof(qword);
	while (p < pEnd)
	{
		*(byte*)p = To;
		p += sizeof(byte);
	}
}

Code: Select all

il void* SetMem(void* pMem, word To, dword Count)
{
	asm volatile(
		"cld\n\t"
		"jecxz 1f\n\t"
		"rep stosb\n\t"
		"1:\n\t"
		"movl %%edx, %%ecx\n\t"
		"test %%edx, %%edx\n\t"
		"jz 2f\n\t"
		"rep stosq\n\t"
		"2:\n\t"
		:
		:"D"(pMem),"c"(Count & 0xF),"d"(Count >> 4),"a"((((qword)To) << 0) | (((qword)To) << 8) | (((qword)To) << 16) | (((qword)To) << 24) | (((qword)To) << 32) | (((qword)To) << 40) | (((qword)To) << 48) | (((qword)To) << 56))
		);
	asm("": : :"%edi","%ecx","cc");

	return pMem;
}

Code: Select all

 1000000:	41 57                	push   r15
 1000002:	48 b8 41 41 41 41 41 	movabs rax,0x4141414141414141     **** 
 1000009:	41 41 41     
 100000c:	ba 00 03 00 00       	mov    edx,0x300   **** 
 1000011:	31 c9                	xor    ecx,ecx    **** 
 1000013:	48 bf 00 f0 02 01 00 	movabs rdi,0x102f000    **** 
 100001a:	00 00 00 
 100001d:	41 56                	push   r14
 100001f:	41 55                	push   r13
 1000021:	41 54                	push   r12
 1000023:	55                   	push   rbp
 1000024:	53                   	push   rbx
 1000025:	48 81 ec 38 03 00 00 	sub    rsp,0x338
 100002c:	fc                   	cld     ****     
 100002d:	67 67 e3 02          	addr64 jecxz 1000033 <_Z11StartKernelv+0x33>   **** 
 1000031:	f3 aa                	rep stos BYTE PTR es:[rdi],al    **** 
 1000033:	89 d1                	mov    ecx,edx   **** 
 1000035:	85 d2                	test   edx,edx    **** 
 1000037:	74 03                	je     100003c <_Z11StartKernelv+0x3c>   **** 
 1000039:	f3 48 ab             	rep stos QWORD PTR es:[rdi],rax   **** 
 100003c:	50                   	push   rax
 100003d:	51                   	push   rcx

Code: Select all

il void* SetMem(void* pMem, word To, dword Count)
{
   asm volatile(
      "cld\n\t"
      "jecxz 1f\n\t"
      "rep stosb\n\t"
      "1:\n\t"
      "movl %%edx, %%ecx\n\t"
      "test %%edx, %%edx\n\t"
      "jz 2f\n\t"
      "rep stosq\n\t"
      "2:\n\t"
      :
      :"D"(pMem),"c"(Count & 0xF),"d"(Count >> 4),"a"((((qword)To) << 0) | (((qword)To) << 8) | (((qword)To) << 16) | (((qword)To) << 24) | (((qword)To) << 32) | (((qword)To) << 40) | (((qword)To) << 48) | (((qword)To) << 56))
      );
   asm("": : :"%edi","%ecx","cc");

   return pMem;
}

Code: Select all

extern "C" void* memset(void * s, int c, size_t count)
{
	byte* b = (byte*)s;

	while (count-- > 0)
		*b++ = c;

	return s;
} 

Code: Select all

1000000:	48 ba 30 78 02 01 00 	movabs rdx,0x1027830
 1000007:	00 00 00 
 100000a:	48 b8 00 f0 02 01 00 	movabs rax,0x102f000
 1000011:	00 00 00 
 1000014:	48 b9 00 20 03 01 00 	movabs rcx,0x1032000
 100001b:	00 00 00 
 100001e:	66 0f 6f 02          	movdqa xmm0,XMMWORD PTR [rdx]
 1000022:	66 0f 7f 00          	movdqa XMMWORD PTR [rax],xmm0
 1000026:	48 83 c0 10          	add    rax,0x10
 100002a:	48 39 c8             	cmp    rax,rcx
 100002d:	75 f3                	jne    1000022 <_Z11StartKernelv+0x22>