Multiplies the lower single-precision, floating-point values of a and b; the upper three single-precision, floating-point values are passed through from a. r0 := a0 * b0; r1 := a1; r2 := a2; r3 := a3 (see _mm_add_ss)
AkSimd.h の 376 行で定義されています。
参照元 AKSIMD_MADD_SS_V4F32().