28.2.35 __builtin_mpy

Description

xptr may be null to signify no X prefetch to be performed, in which case the values of xincr and xval are ignored, but required.

yptr may be null to signify no Y prefetch to be performed, in which case the values of yincr and yval are ignored, but required.

xval and yval nominate the address of a C variable where the prefetched value will be stored.

xincr and yincr may be the literal values: -6, -4, -2, 0, 2, 4, 6 or an integer value.

For example:

 volatile register int result asm("A");
 int *xmemory;
 int *ymemory;
 int xVal, yVal;

 result = __builtin_mpy(xVal, yVal, &xmemory, &xVal, 2, &ymemory, &yVal, 2);

might generate:

mpy w4*w5, A, [w8]+=2, w4, [w10]+=2, w5

Prototype

int __builtin_mpy(int a, int b,
 int **xptr, int *xval, int xincr,
 int **yptr, int *yval, int yincr);

Argument

a – Integer multiplicand.

b – Integer multiplier.

xptr – Integer pointer to pointer to x prefetch.

xval – Integer pointer to value of x prefetch.

xincr – Integer increment value of x prefetch.

yptr – Integer pointer to pointer to y prefetch.

yval – Integer pointer to value of y prefetch.

yincr – Integer increment value of y prefetch.

AWB – Integer pointer to accumulator selection.

Return Value

Returns the value of a x b.

Assembler Operator/ Machine Instruction

mpy

Error Messages

An error message will be displayed if:

• the result is not an accumulator register
• xval is a null value but xptr is not null
• yval is a null value but yptr is not null