User guide

Writing the multiply routine in C:

// long multiply routine in C

long long smull(int x, int y)

{

return (long long) x * (long long) y;

}

The compiler generates the following code:

MOV r2,r0

MOV r0,r1

MOV r1,r2

SMULL r12,r1,r0,r2

MOV r0,r12

MOV pc,lr

r12 is corrupted in this routine. This is allowed under ATPCS.

Example 4-5 Multiply in inline assembly language

Writing the same routine using inline assembly language:

long long smull(int x, int y)

{

long long res;

__asm { SMULL ((int*)&res)[0], ((int*)&res)[1], x, y }

return res;

}

The compiler generates the following code:

MOV r2,r0

SMULL r0,r1,r2,r1

MOV pc,lr

Mixing C, C++, and Assembly Language