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Fast multiply.

This commit is contained in:
George Norton 2023-08-21 01:13:24 +01:00
parent 59d7c2adc4
commit f9a2b6efa4
2 changed files with 9 additions and 22 deletions
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28
firmware/code/fix16.inl
View File

@ -85,25 +85,11 @@ static inline fix3_28_t fix3_28_from_dbl(double a) {
/// @param inArg1 Q3.28 format fixed point number. /// @param inArg1 Q3.28 format fixed point number.
/// @return A Q3.28 fixed point number that represents the truncated result of inArg0 x inArg1. /// @return A Q3.28 fixed point number that represents the truncated result of inArg0 x inArg1.
static inline fix3_28_t fix16_mul(fix3_28_t inArg0, fix3_28_t inArg1) { static inline fix3_28_t fix16_mul(fix3_28_t inArg0, fix3_28_t inArg1) {
const int64_t product = (int64_t)inArg0 * inArg1; int32_t A = (inArg0 >> 14), C = (inArg1 >> 14);
uint32_t B = (inArg0 & 0x3FFF), D = (inArg1 & 0x3FFF);
/* Since we're expecting 2 Q3.28 numbers, the multiplication result should be a Q7.56 number. int32_t AC = A*C;
To bring this number back to the right order of magnitude, we need to shift int32_t AD_CB = A*D + C*B;
it to the right by 28. */ product_hi = AC + (AD_CB >> 14);
fix3_28_t result = product >> 28; // Carry not handled.
return product_hi;
// Handle rounding where we are choppping off low order bits
// Disabled for now, too much load. We get crackling when adjusting
// the volume.
#if 0
if (product & 0x4000) {
if (result >= 0) {
result++;
}
else {
result--;
}
}
#endif
return result;
} }

3
firmware/code/run.c
View File

@ -124,8 +124,9 @@ static void __no_inline_not_in_flash_func(_as_audio_packet)(struct usb_endpoint
int32_t *out = (int32_t *) userbuf; int32_t *out = (int32_t *) userbuf;
int samples = usb_buffer->data_len / 2; int samples = usb_buffer->data_len / 2;
const fix3_28_t preamp = preprocessing.preamp;
for (int i = 0; i < samples; i ++) { for (int i = 0; i < samples; i ++) {
out[i] = fix16_mul(norm_fix3_28_from_s16sample(in[i]), preprocessing.preamp); out[i] = fix16_mul(norm_fix3_28_from_s16sample(in[i]), preamp);
} }
// keep on truckin' // keep on truckin'