> From: Grant Edwards
> Newsgroups: gmane.comp.hardware.texas-instruments.msp430.gcc.user
> Subject: Question about libgcc 16x16=>32 multiply
> Date: Thu, 22 Mar 2007 20:23:28 +0000 (UTC)
Hallo.
> uint32_t r;
>
> void foo(uint16_t u1, uint16_t u2)
> {
> r = (uint32_t)u1 * (uint32_t)u2;
> }
>
>
> I've been looking at the code for the case above:
>
> 1 foo:
> 2 push r11
> 3 push r10
> 4 mov r15, r10
> 5 mov r14, r12
> 6 clr r11
> 7 clr r13
> 8 call #__umulhisi3
> 9 mov r14, &_r
> 10 mov r15, &_r+2
> 11 pop r10
> 12 pop r11
> 13 ret
>
>
> I've noticed that even though a 16x16 multiply is being called,
As i'm new on all this, i just note, that function names are very
strange.
> the two operands are being passed as 32-bit values.
And this is, what your C expression tells, no?
> Why pass two 32 bit values to a library function who's purpose is to
> multiply two 16 bit values? IOW why are lines 6 and 7 there?
file gcc/config/msp430/libgcc.S:
...
.global __umulhisi3
.func __umulhisi3
__umulhisi3:
br #__mulsi3
...
/*******************************************************
Multiplication 32 x 32
*******************************************************/
...
.global __mulsi3
.func __mulsi3
__mulsi3:
Thus, it seems 32x32 instead.
____
