[Mspgcc-users] Question about libgcc 16x16=>32 multiply

[Grant Edwards]

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,
the two operands are being passed as 32-bit values.  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?

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