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Increase the max fix16 size to -32.0..32.0 as it seems it is possible to create coefficients which are >16.

This commit is contained in:
George Norton 2023-06-22 20:46:58 +01:00
parent 6c627d22fd
commit cf95f18880
2 changed files with 10 additions and 9 deletions
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9
firmware/code/fix16.c
View File

@ -61,15 +61,15 @@ fix16_t fix16_mul(fix16_t inArg0, fix16_t inArg1) {
}
#else
fix16_t fix16_from_s16sample(int16_t a) {
return a * fix16_one_normalized;
return a * fix16_lsb;
}
int16_t fix16_to_s16sample(fix16_t a) {
// Handle rounding up front, adding one can cause an overflow/underflow
if (a < 0) {
a -= (fix16_one_normalized >> 1);
a -= (fix16_lsb >> 1);
} else {
a += (fix16_one_normalized >> 1);
a += (fix16_lsb >> 1);
}
// Saturate the value if an overflow has occurred
@ -100,9 +100,10 @@ double fix16_to_dbl(fix16_t a) {
// We work in 64bits then shift the result to get
// the bit representing 1 back into the correct position.
// i.e. 1*1 == 1, so 20000000^2 >> 25 = 20000000
fix16_t fix16_mul(fix16_t inArg0, fix16_t inArg1) {
const int64_t product = (int64_t)inArg0 * inArg1;
fix16_t result = product >> 29;
fix16_t result = product >> 25;
// Handle rounding where we are choppping off low order bits
// Disabled for now, too much load. We get crackling when adjusting
// the volume.

10
firmware/code/fix16.h
View File

@ -30,18 +30,18 @@
#ifdef USE_DOUBLE
typedef double fix16_t;
static const fix16_t fix16_zero = 0;
static const fix16_t fix16_one = 1;
#else
// We normalize all values into the range -1..1 with 1 extra bit for overflows
// We normalize all values into the range -32..32 with 1 extra bit for overflows
// and one bit for the sign. We allow fixed point values to overflow, but they
// are clipped at the point they are written back to a s16sample.
//
// The reason for normalizing the samples is because the filter coefficients are
// small (usually in the range -1..1), by normalizing everything the coefficients
// small (usually well within in the range -32..32), by normalizing everything the coefficients
// get lots of additional bits of precision.
typedef int32_t fix16_t;
static const fix16_t fix16_overflow = 0x80000000;
static const fix16_t fix16_one_normalized = 0x00008000;
static const fix16_t fix16_one = 0x20000000;
static const fix16_t fix16_lsb = 0x8000;
static const fix16_t fix16_one = 0x002000000;
static const fix16_t fix16_zero = 0x00000000;
#endif