Function core_arch::x86::_mm_floor_sd

pub unsafe fn _mm_floor_sd(a: __m128d, b: __m128d) -> __m128d

This is supported on x86 and target feature sse4.1 only.

Round the lower double-precision (64-bit) floating-point element in b down to an integer value, store the result as a double-precision floating-point element in the lower element of the intrinsic result, and copies the upper element from a to the upper element of the intrinsic result.

Intel's documentation