Is there hardware support for 128bit integers in modern processors?

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The x86-64 instruction set can do 64-bit*64-bit to 128-bit using one instruction (mul for unsigned imul for signed each with one operand) so I would argue that to some degree that the x86 instruction set does include some support for 128-bit integers.

If your instruction set does not have an instruction to do 64-bit*64-bit to 128-bit then you need several instructions to emulate this.

This is why 128-bit * 128-bit to lower 128-bit operations can be done with few instructions with x86-64. For example with GCC

__int128 mul(__int128 a, __int128 b) {
    return a*b;
}

produces this assembly 

imulq   %rdx, %rsi
movq    %rdi, %rax
imulq   %rdi, %rcx
mulq    %rdx
addq    %rsi, %rcx
addq    %rcx, %rdx

which uses one 64-bit * 64-bit to 128-bit instructions, two 64-bit * 64-bit to lower 64-bit instructions, and two 64-bit additions.

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