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Transceiver52M: Setup sinc() call directly with table lookup 

On Beagle Board the call into the sinc() function is generating a lot of
load on the peak interpolation. Simplify the sinc() function with a
dedicated table lookup. Eventually, this table may be removed in favour
of using a precomputed filterbank for fractional delay determination.

Signed-off-by: Thomas Tsou <tom@tsou.cc>
This commit is contained in:
Thomas Tsou 2013-11-09 22:08:51 -05:00
parent d0f3ca3e94
commit 0e0e1f4363
1 changed files with 23 additions and 2 deletions
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25
Transceiver52M/sigProcLib.cpp
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@ -43,6 +43,7 @@ using namespace GSM;
/** Lookup tables for trigonometric approximation */
float cosTable[TABLESIZE+1]; // add 1 element for wrap around
float sinTable[TABLESIZE+1];
float sincTable[TABLESIZE+1];
/** Constants */
static const float M_PI_F = (float)M_PI;
@ -821,10 +822,29 @@ signalVector *modulateBurst(const BitVector &wBurst, int guardPeriodLength,
return modulateBurstBasic(wBurst, guardPeriodLength, sps);
}
void generateSincTable()
{
float x;
for (int i = 0; i < TABLESIZE; i++) {
x = (float) i / TABLESIZE * 8 * M_PI;
if (fabs(x) < 0.01) {
sincTable[i] = 1.0f;
continue;
}
sincTable[i] = sinf(x) / x;
}
}
float sinc(float x)
{
if ((x >= 0.01F) || (x <= -0.01F)) return (sinLookup(x)/x);
return 1.0F;
if (fabs(x) >= 8 * M_PI)
return 0.0;
int index = (int) floorf(fabs(x) / (8 * M_PI) * TABLESIZE);
return sincTable[index];
}
/*
@ -1685,6 +1705,7 @@ bool sigProcLibSetup(int sps)
return false;
initTrigTables();
generateSincTable();
initGMSKRotationTables(sps);
GSMPulse1 = generateGSMPulse(1, 2);