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GCC and Clang have the __int128_t and __uint128_t extensions for 128-bit integer arithmetic.
I was hopeful that __m128i would give something similar for the Intel C Compiler, but (if it's even possible) it looks to me like I'd have to write explicit SSE2 function calls in order to use __m128i, instead of using "built-in" operators like +, -, *, /, and %. I was hoping to do something like this (this doesn't work):
#if defined(__INTEL_COMPILER) && defined(__SSE2__)
#include "xmmintrin.h"
typedef __u128 uint128_t;
#elif defined (__GNUC__)
typedef __uint128_t uint128_t;
#else
#error For 128-bit arithmetic we need GCC or ICC, or uint128_t
#endif
Is there 128-bit integer support with the operators +, -, *, /, and % somewhere buried in icc?
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In the same way that compilers emulate e.g. 64-bit integer arithmetic on architectures with register sizes less than 64 bits, some compilers also support 128-bit integer arithmetic. For example, the GCC C compiler 4.6 and later has a 128-bit integer type __int128 for some architectures.
The 128-bit data type can handle up to 31 significant digits (compared to 17 handled by the 64-bit long double). However, while this data type can store numbers with more precision than the 64-bit data type, it does not store numbers of greater magnitude.
DrinkMoreBoilingWater's blog. As an extension the integer scalar type __int128 is supported for targets which have an integer mode wide enough to hold 128 bits. Simply write __int128 for a signed 128-bit integer, or unsigned __int128 for an unsigned 128-bit integer.
The int128 type defines a signed 128-bit integer. The API is meant to mimic an intrinsic integer type as closely as possible, so that any forthcoming int128_t can be a drop-in replacement. The int128 type supports the following: Implicit conversion from signed integral types and unsigned types narrower than 128 bits.
From what I can tell, at least icc 13.0.1+ support __int128_t and __uint128_t. Courtesy of Matt Godbolt's Compiler Explorer:
__int128_t ai (__int128_t x, __int128_t y) {
return x + y;
}
__int128_t mi (__int128_t x, __int128_t y) {
return x * y;
}
__int128_t di (__int128_t x, __int128_t y) {
return x / y;
}
__int128_t ri (__int128_t x, __int128_t y) {
return x % y;
}
compiles to:
L__routine_start_ai_0:
ai:
add rdi, rdx #2.14
mov rax, rdi #2.14
adc rsi, rcx #2.14
mov rdx, rsi #2.14
ret #2.14
L__routine_start_mi_1:
mi:
mov rax, rdi #6.14
imul rsi, rdx #6.14
imul rcx, rdi #6.14
mul rdx #6.14
add rsi, rcx #6.14
add rdx, rsi #6.14
ret #6.14
L__routine_start_di_2:
di:
push rsi #9.44
call __divti3 #10.14
pop rcx #10.14
ret #10.14
L__routine_start_ri_3:
ri:
push rsi #13.44
call __modti3 #14.14
pop rcx #14.14
ret #14.14
with icc 13.0.1 (http://goo.gl/UnxEFt).
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