28.2.45 __builtin_mpyn

Description

Computes -a x b ; 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.

For example:

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

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

might generate:

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

Prototype

int16_t __builtin_mpyn(int16_t a, int16_t b,
 int16_t **xptr, int16_t *xval, int16_t xincr,
 int16_t **yptr, int16_t *yval, int16_t yincr);

Arguments

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.

Machine Instruction

mpyn

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