xvmsubadp
VSX Vector Multiply-Subtract Type-A Double-Precision
Performs a double-precision floating-point multiply-subtract operation on vector elements.
Details
Performs a vector multiply-subtract operation on double-precision floating-point elements, computing XT = XT - (XA × XB) for each element. The operation is fused, rounding only once at the end. This instruction requires VSX support and updates FPSCR exception flags based on the operation results.
Pseudocode Operation
for i ∈ {0, 1}
XT[i*64:(i+1)*64] ← XT[i*64:(i+1)*64] - (XA[i*64:(i+1)*64] × XB[i*64:(i+1)*64])
FPSCR ← update_exception_flags(FPSCR, results)Programming Note
The xvmsubadp instruction is commonly used for complex floating-point arithmetic operations involving multiplication, subtraction, and addition. Ensure that the VSX (Vector Scalar Extensions) are enabled in the MSR register to avoid a VSX_Unavailable exception. Be cautious of potential exceptions such as VXSNAN, VXIMZ, VXISI, OX, UX, and XX, which can be triggered by invalid operations or overflow conditions. The instruction operates on double-precision floating-point numbers and requires proper alignment of the input vectors.
Example
Encoding
Operands
-
XT
Target Vector Register -
XA
Source Vector Register -
XB
Source Vector Register