28.2.40 __builtin_mac

Description

Computes a x b and sums with accumulator; also prefetches data ready for a future MAC operation.

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.

If AWB is non null, the other accumulator will be written back into the referenced variable.

For example:

 volatile register int16_t result asm("A");
 volatile register int16_t B asm("B");
 int16_t *xmemory;
 int16_t *ymemory;
 int16_t xVal, yVal;

 result = __builtin_mac(result, xVal, yVal, &xmemory, &xVal, 2, &ymemory, &yVal, 2, 0, B);

might generate:

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

Prototype

int16_t __builtin_mac(int16_t Accum, int16_t a, int16_t b, 
 int16_t **xptr, int16_t *xval, int16_t xincr, 
 int16_t **yptr, int16_t *yval, int16_t yincr, 
 int16_t *AWB, int16_t AWB_accum);