[linux][memory]memcmp几种实现和性能对比

int memcmp(const void *cs, const void *ct, size_t count)
{
    const unsigned char *su1, *su2;
    int res = 0;
    for (su1 = cs, su2 = ct; 0 < count; ++su1, ++su2, count--)
        if ((res = *su1 - *su2) != 0)
            break;
    return res;
}

int memcmpx86_64(void *s1, void *s2, size_t n)
{
    size_t num = n / 8;
    register int res;
    __asm__ __volatile__
    (
     "testq %q3,%q3nt"
     "repe; cmpsqnt"
     "je        1fnt"
     "sbbq      %q0,%q0nt"
     "orq       $1,%q0n"
     "1:"
     : "=&a" (res), "+&S" (s1), "+&D" (s2), "+&c" (num)
     : "0" (0)
     : "cc");
    return res;
}

ENTRY (memcmp)
    test    %rdx, %rdx
    jz  L(finz)
    cmpq    $1, %rdx
    jle L(finr1b)
    subq    %rdi, %rsi
    movq    %rdx, %r10
    cmpq    $32, %r10
    jge L(gt32)
    /* Handle small chunks and last block of less than 32 bytes.  */
L(small):
    testq   $1, %r10
    jz  L(s2b)
    movzbl  (%rdi), %eax
    movzbl  (%rdi, %rsi), %edx
    subq    $1, %r10
    je  L(finz1)
    addq    $1, %rdi
    subl    %edx, %eax
    jnz L(exit)
L(s2b):
    testq   $2, %r10
    jz  L(s4b)
    movzwl  (%rdi), %eax
    movzwl  (%rdi, %rsi), %edx
    subq    $2, %r10
    je  L(fin2_7)
    addq    $2, %rdi
    cmpl    %edx, %eax
    jnz L(fin2_7)
L(s4b):
    testq   $4, %r10
    jz  L(s8b)
    movl    (%rdi), %eax
    movl    (%rdi, %rsi), %edx
    subq    $4, %r10
    je  L(fin2_7)
    addq    $4, %rdi
    cmpl    %edx, %eax
    jnz L(fin2_7)
L(s8b):
    testq   $8, %r10
    jz  L(s16b)
    movq    (%rdi), %rax
    movq    (%rdi, %rsi), %rdx
    subq    $8, %r10
    je  L(fin2_7)
    addq    $8, %rdi
    cmpq    %rdx, %rax
    jnz L(fin2_7)
L(s16b):
    movdqu    (%rdi), %xmm1
    movdqu    (%rdi, %rsi), %xmm0
    pcmpeqb   %xmm0, %xmm1
    pmovmskb  %xmm1, %edx
    xorl      %eax, %eax
    subl      $0xffff, %edx
    jz    L(finz)
    bsfl      %edx, %ecx
    leaq     (%rdi, %rcx), %rcx
    movzbl   (%rcx), %eax
    movzbl   (%rsi, %rcx), %edx
    jmp  L(finz1)
    .p2align 4,, 4
L(finr1b):
    movzbl  (%rdi), %eax
    movzbl  (%rsi), %edx
L(finz1):
    subl    %edx, %eax
L(exit):
    ret
    .p2align 4,, 4
L(fin2_7):
    cmpq    %rdx, %rax
    jz  L(finz)
    movq    %rax, %r11
    subq    %rdx, %r11
    bsfq    %r11, %rcx
    sarq    $3, %rcx
    salq    $3, %rcx
    sarq    %cl, %rax
    movzbl  %al, %eax
    sarq    %cl, %rdx
    movzbl  %dl, %edx
    subl    %edx, %eax
    ret
    .p2align 4,, 4
L(finz):
    xorl    %eax, %eax
    ret
    /* For blocks bigger than 32 bytes
       1. Advance one of the addr pointer to be 16B aligned.
       2. Treat the case of both addr pointers aligned to 16B
          separately to avoid movdqu.
       3. Handle any blocks of greater than 64 consecutive bytes with
          unrolling to reduce branches.
       4. At least one addr pointer is 16B aligned, use memory version
          of pcmbeqb.
    */
    .p2align 4,, 4
L(gt32):
    movq    %rdx, %r11
    addq    %rdi, %r11
    movq    %rdi, %r8
    andq    $15, %r8
    jz  L(16am)
    /* Both pointers may be misaligned.  */
    movdqu  (%rdi), %xmm1
    movdqu  (%rdi, %rsi), %xmm0
    pcmpeqb   %xmm0, %xmm1
    pmovmskb  %xmm1, %edx
    subl      $0xffff, %edx
    jnz       L(neq)
    neg  %r8
    leaq    16(%rdi, %r8), %rdi
L(16am):
    /* Handle two 16B aligned pointers separately.  */
    testq   $15, %rsi
    jz      L(ATR)
    testq   $16, %rdi
    jz  L(A32)
    movdqu  (%rdi, %rsi), %xmm0
    pcmpeqb   (%rdi), %xmm0
    pmovmskb  %xmm0, %edx
    subl      $0xffff, %edx
    jnz       L(neq)
    addq    $16, %rdi
L(A32):
    movq    %r11, %r10
    andq    $-32, %r10
    cmpq    %r10, %rdi
        jge L(mt16)
    /* Pre-unroll to be ready for unrolled 64B loop.  */
    testq   $32, %rdi
    jz  L(A64)
    movdqu    (%rdi,%rsi), %xmm0
    pcmpeqb   (%rdi), %xmm0
    pmovmskb  %xmm0, %edx
    subl      $0xffff, %edx
    jnz       L(neq)
    addq       $16, %rdi
    movdqu    (%rdi,%rsi), %xmm0
    pcmpeqb  (%rdi), %xmm0
    pmovmskb  %xmm0, %edx
    subl      $0xffff, %edx
    jnz       L(neq)
    addq       $16, %rdi
L(A64):
    movq    %r11, %r10
    andq    $-64, %r10
    cmpq    %r10, %rdi
        jge L(mt32)
L(A64main):
    movdqu    (%rdi,%rsi), %xmm0
    pcmpeqb   (%rdi), %xmm0
    pmovmskb  %xmm0, %edx
    subl      $0xffff, %edx
    jnz       L(neq)
    addq       $16, %rdi
    movdqu    (%rdi,%rsi), %xmm0
    pcmpeqb   (%rdi), %xmm0
    pmovmskb  %xmm0, %edx
    subl      $0xffff, %edx
    jnz       L(neq)
    addq       $16, %rdi
    movdqu    (%rdi,%rsi), %xmm0
    pcmpeqb   (%rdi), %xmm0
    pmovmskb  %xmm0, %edx
    subl      $0xffff, %edx
    jnz       L(neq)
    addq       $16, %rdi
    movdqu    (%rdi,%rsi), %xmm0
    pcmpeqb  (%rdi), %xmm0
    pmovmskb  %xmm0, %edx
    subl      $0xffff, %edx
    jnz       L(neq)
    addq       $16, %rdi
    cmpq       %rdi, %r10
    jne       L(A64main)
L(mt32):
    movq    %r11, %r10
    andq    $-32, %r10
    cmpq    %r10, %rdi
        jge L(mt16)
L(A32main):
    movdqu    (%rdi,%rsi), %xmm0
    pcmpeqb   (%rdi), %xmm0
    pmovmskb  %xmm0, %edx
    subl      $0xffff, %edx
    jnz       L(neq)
    addq       $16, %rdi
    movdqu    (%rdi,%rsi), %xmm0
    pcmpeqb  (%rdi), %xmm0
    pmovmskb  %xmm0, %edx
    subl      $0xffff, %edx
    jnz       L(neq)
    addq       $16, %rdi
    cmpq       %rdi, %r10
    jne       L(A32main)
L(mt16):
    subq       %rdi, %r11
    je    L(finz)
    movq      %r11, %r10
    jmp   L(small)
    .p2align 4,, 4
L(neq):
    bsfl      %edx, %ecx
    movzbl   (%rdi, %rcx), %eax
    addq     %rdi, %rsi
    movzbl   (%rsi,%rcx), %edx
    jmp  L(finz1)
    .p2align 4,, 4
L(ATR):
    movq    %r11, %r10
    andq    $-32, %r10
    cmpq    %r10, %rdi
        jge L(mt16)
    testq   $16, %rdi
    jz  L(ATR32)
    movdqa    (%rdi,%rsi), %xmm0
    pcmpeqb   (%rdi), %xmm0
    pmovmskb  %xmm0, %edx
    subl      $0xffff, %edx
    jnz       L(neq)
    addq       $16, %rdi
    cmpq       %rdi, %r10
    je       L(mt16)
L(ATR32):
    movq    %r11, %r10
    andq    $-64, %r10
    testq   $32, %rdi
    jz  L(ATR64)
    movdqa    (%rdi,%rsi), %xmm0
    pcmpeqb   (%rdi), %xmm0
    pmovmskb  %xmm0, %edx
    subl      $0xffff, %edx
    jnz       L(neq)
    addq       $16, %rdi
    movdqa    (%rdi,%rsi), %xmm0
    pcmpeqb   (%rdi), %xmm0
    pmovmskb  %xmm0, %edx
    subl      $0xffff, %edx
    jnz       L(neq)
    addq       $16, %rdi
L(ATR64):
    cmpq       %rdi, %r10
    je     L(mt32)
L(ATR64main):
    movdqa    (%rdi,%rsi), %xmm0
    pcmpeqb   (%rdi), %xmm0
    pmovmskb  %xmm0, %edx
    subl      $0xffff, %edx
    jnz       L(neq)
    addq       $16, %rdi
    movdqa    (%rdi,%rsi), %xmm0
    pcmpeqb   (%rdi), %xmm0
    pmovmskb  %xmm0, %edx
    subl      $0xffff, %edx
    jnz       L(neq)
    addq       $16, %rdi
    movdqa    (%rdi,%rsi), %xmm0
    pcmpeqb   (%rdi), %xmm0
    pmovmskb  %xmm0, %edx
    subl      $0xffff, %edx
    jnz       L(neq)
    addq       $16, %rdi
    movdqa    (%rdi,%rsi), %xmm0
    pcmpeqb   (%rdi), %xmm0
    pmovmskb  %xmm0, %edx
    subl      $0xffff, %edx
    jnz       L(neq)
    addq       $16, %rdi
    cmpq       %rdi, %r10
    jne       L(ATR64main)
    movq    %r11, %r10
    andq    $-32, %r10
    cmpq    %r10, %rdi
        jge L(mt16)
L(ATR32res):
    movdqa    (%rdi,%rsi), %xmm0
    pcmpeqb   (%rdi), %xmm0
    pmovmskb  %xmm0, %edx
    subl      $0xffff, %edx
    jnz       L(neq)
    addq       $16, %rdi
    movdqa    (%rdi,%rsi), %xmm0
    pcmpeqb   (%rdi), %xmm0
    pmovmskb  %xmm0, %edx
    subl      $0xffff, %edx
    jnz       L(neq)
    addq       $16, %rdi
    cmpq      %r10, %rdi
    jne       L(ATR32res)
    subq       %rdi, %r11
    je    L(finz)
    movq      %r11, %r10
    jmp   L(small)
    /* Align to 16byte to improve instruction fetch.  */
    .p2align 4,, 4
END(memcmp)
4，unsigned long memcmp
方法1修改一下，单次比较unsigned long的长度。
int kmemcmp(const void *cs, const void *ct, size_t count)
{
    const unsigned long *su1, *su2;
    int res = 0;
    for (su1 = cs, su2 = ct; 0 < count;) {
        if ((res = *su1 - *su2) != 0)
            break;
        su1 += 1;//sizeof(unsigned long);
        su2 += 1;//sizeof(unsigned long);
        count -= sizeof(unsigned long);
    }
    return res;
}