• State Not Answered
  • Locked Locked
  • Replies 6 replies
  • Subscribers 20 subscribers
  • Views 1835 views
  • Users 0 members are here
Options
How was your experience today?
This discussion has been locked.
You can no longer post new replies to this discussion. If you have a question you can start a new discussion

Getting the compiler to consistently use LDM ?

Christoph Franck

Hello,

I am trying to optimize the implementation of a FIR filter. One major improvement would be to use LDM for loading all data/coefficients to minimize the amount of cycles used for memory access.

How can I get the compiler do this consistently ?

long fir_coef[] = ...;
long dbuf = ...;
long out_buf;

void test(void)
{
register long c1, c2, c3, c4;
register long d1, d2, d3, d4;
registerlong accu;

c1 = fir_coef[0];
c2 = fir_coef[1];
c3 = fir_coef[2];
c4 = fir_coef[3];
d1 = dbuf[0];
d2 = dbuf[1];
d3 = dbuf[2];
d4 = dbuf[3];

accu = 0;
accu += c1 * d1;
accu += c2 * d2;
accu += c3 * d3;
accu += c4 * d4;

out_buf = accu;
}

seems to use LDM sporadically to load two registers at once (at -O3), but ideally I would like to see only two LDM instructions in the above code.

Can this be done in C, or is it time to get out the assembler ?

0