comment on

C code:

typedef __int128 int128_t;

int128_t
add128(int128_t a, int128_t b) {
  return a + b;
}

int128_t
sub128(int128_t a, int128_t b) {
  return a - b;
}

int128_t
mul128(int128_t a, int128_t b) {
  return a * b;
}

int128_t
div128(int128_t a, int128_t b) {
  return a / b;
}

int128_t
rem128(int128_t a, int128_t b) {
  return a % b;
}
[download]

Assembler generated by gcc -O3 -march=core2:

    .file    "lookatme.c"
    .text
    .p2align 4,,15
    .globl    add128
    .type    add128, @function
add128:
.LFB0:
    .cfi_startproc
    movq    %rdx, %rax
    movq    %rcx, %rdx
    addq    %rdi, %rax
    adcq    %rsi, %rdx
    ret
    .cfi_endproc
.LFE0:
    .size    add128, .-add128
    .p2align 4,,15
    .globl    sub128
    .type    sub128, @function
sub128:
.LFB1:
    .cfi_startproc
    movq    %rsi, %r10
    movq    %rdi, %rsi
    subq    %rdx, %rsi
    movq    %r10, %rdi
    sbbq    %rcx, %rdi
    movq    %rsi, %rax
    movq    %rdi, %rdx
    ret
    .cfi_endproc
.LFE1:
    .size    sub128, .-sub128
    .p2align 4,,15
    .globl    mul128
    .type    mul128, @function
mul128:
.LFB2:
    .cfi_startproc
    imulq    %rdx, %rsi
    movq    %rdx, %rax
    imulq    %rdi, %rcx
    mulq    %rdi
    addq    %rcx, %rsi
    addq    %rsi, %rdx
    ret
    .cfi_endproc
.LFE2:
    .size    mul128, .-mul128
    .globl    __divti3
    .p2align 4,,15
    .globl    div128
    .type    div128, @function
div128:
.LFB3:
    .cfi_startproc
    subq    $8, %rsp
    .cfi_def_cfa_offset 16
    call    __divti3
    addq    $8, %rsp
    .cfi_def_cfa_offset 8
    ret
    .cfi_endproc
.LFE3:
    .size    div128, .-div128
    .globl    __modti3
    .p2align 4,,15
    .globl    rem128
    .type    rem128, @function
rem128:
.LFB4:
    .cfi_startproc
    subq    $8, %rsp
    .cfi_def_cfa_offset 16
    call    __modti3
    addq    $8, %rsp
    .cfi_def_cfa_offset 8
    ret
    .cfi_endproc
.LFE4:
    .size    rem128, .-rem128
    .ident    "GCC: (GNU) 4.6.0 20110207 (experimental) [trunk revisio
+n 169884]"
    .section    .note.GNU-stack,"",@progbits
[download]

So, it uses inlined 64bits arithmetic, except for division and modulo operations that are library calls.

In reply to Re^8: Module for 128-bit integer math? by salva
in thread Module for 128-bit integer math? by BrowserUk

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