mmaddps

mmaddps is an MMX/SSE instruction that performs a multiply-add operation on packed single-precision floating-point values. Given two 128-bit operands containing four 32-bit floats each, it multiplies corresponding elements and adds adjacent products to produce two 32-bit results embedded in the destination.

Formally, for operand vectors a = [a0, a1, a2, a3] and b = [b0, b1, b2, b3], mmaddps computes [a0*b0 + a1*b1, a2*b2 + a3*b3] and places the results in the two lower 32-bit lanes of the destination register. The remaining two lanes are unspecified by the instruction and should be treated as undefined unless overwritten by subsequent instructions. The operation uses 4 multiplies and 2 additions per 128-bit vector.

mmaddps is part of the MMX instruction set and has an equivalent SSE form called maddps when operating on XMM registers. In C intrinsics, the corresponding intrinsic is _mm_madd_ps (or an equivalent for the specific compiler/headers). The two results produced effectively perform two parallel 2-element dot products in a single instruction, contributing to performance in vectorized computations.

Typical use cases include dot-product style computations in graphics, digital signal processing, and physics simulations where two small 2-element dot products are computed per iteration. Notes include IEEE-754 compliance for floating-point operations and the need to manage MMX state explicitly (for example, using EMMS to clear the MMX state before switching back to SSE).