# Vault 7: Projects

This publication series is about specific projects related to the Vault 7 main publication.

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# PIC24FJ64GA004 - Programmers Reference Manual

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© 2005-2011 Microchip Technology Inc. DS70157F-page 465
Section 6. Built-in Functions
Built-in Functions
6
__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:
register int result asm("A");
int *xmemory;
int *ymemory;
int xVal, yVal;
result = _ _builtin_mpy(xVal, yVal,
&xmemory, &xVal, 2,
&ymemory, &yVal, 2);
May generate:
mac w4*w5, A, [w8]+=2, w4, [w10]+=2, w5
Prototype:
int _ _builtin_mpyn(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.
Note: The arguments xptr and yptr must point to the arrays located in the x data
memory and y data memory, respectively.
Return Value:
Returns the cleared value result to an accumulator.
Assembler Operator / Machine Instruction:
mpyn
Error Messages:
An error message appears 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

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