vmsumubm
Vector Multiply-Sum Unsigned Byte Modulo
Multiplies bytes and sums adjacent results into words.
Details
Multiplies each unsigned byte in vA by the corresponding byte in vB, then sums the products of adjacent byte pairs to produce four unsigned 32-bit word results. The results are added to the four words in the accumulator vC and stored in vD. This is a VMX (AltiVec) instruction that does not affect condition or status flags.
Pseudocode Operation
vD[0:31] ← (vA[0:7] × vB[0:7]) + (vA[8:15] × vB[8:15]) + vC[0:31]
vD[32:63] ← (vA[16:23] × vB[16:23]) + (vA[24:31] × vB[24:31]) + vC[32:63]
vD[64:95] ← (vA[32:39] × vB[32:39]) + (vA[40:47] × vB[40:47]) + vC[64:95]
vD[96:127] ← (vA[48:55] × vB[48:55]) + (vA[56:63] × vB[56:63]) + vC[96:127]Programming Note
This instruction is commonly used for performing efficient vectorized operations on unsigned byte data. Ensure that the Vector Facility (MSR.VEC) is enabled before using this instruction; otherwise, a Vector_Unavailable exception will be raised. The operation processes 8 bytes per iteration, multiplying corresponding elements and adding to the third source vector's word element, storing the result in the destination vector. Be cautious of overflow as only the low-order 16 bits are stored.
Example
Encoding
Operands
-
vD
Target -
vA
Src A -
vB
Src B -
vC
Accumulator