Changed methode of mean power calculation.

Corrects loose in precision, slight performance gain.
Mictronics · Feb 23, 2017 · 2e5c4a0 · 2e5c4a0
1 parent 4aab0f8
commit 2e5c4a0
Showing 1 changed file with 30 additions and 21 deletions.
diff --git a/convert.c b/convert.c
@@ -66,7 +66,6 @@ static void convert_uc8_nodc(void *iq_data,
  uint16_t *in = iq_data;
  unsigned i;
  uint64_t sum_level = 0;
- uint64_t sum_power = 0;
  uint16_t mag;
 
  MODES_NOTUSED(state);
@@ -77,7 +76,6 @@ static void convert_uc8_nodc(void *iq_data,
  mag = uc8_lookup[*in++]; \
  *mag_data++ = mag; \
  sum_level += mag; \
- sum_power += (uint32_t)mag * (uint32_t)mag; \
  } while(0)
 
  // unroll this a bit
@@ -102,8 +100,26 @@ static void convert_uc8_nodc(void *iq_data,
  *out_mean_level = sum_level / 65536.0 / nsamples;
  }
 
+ /* We already have the average mean level so calculate power from it.
+ * Example from live data:
+ * sum_level = 91873866
+ * out_mean_level = 0.010695526
+ * Level to dB is: 20*log(out_mean_level) = 20*log(0.010695526) = -39.416 dB
+ * 
+ * Old:
+ * sum_power = 85686914156
+ * out_mean_power = 0.00015221812
+ * Power to dB is: 10*log(out_mean_power) = 10*log(0.00015221812) = -38.175 dB
+ * Converting this power back to level results in 0.0123377 so it's not
+ * equal to square level (or magnitude).
+ * 
+ * New:
+ * out_mean_power = out_mean_level^2 = 0.000114394
+ * Power to dB is: 10*log(out_mean_power) = 10*log(0.000114394) = -39.416 dB
+ * 
+ */
  if (out_mean_power) {
- *out_mean_power = sum_power / 65535.0 / 65535.0 / nsamples;
+ *out_mean_power = *out_mean_level * *out_mean_level;
  }
 }
 
@@ -123,7 +139,7 @@ static void convert_uc8_generic(void *iq_data,
  unsigned i;
  uint8_t I, Q;
  float fI, fQ, magsq;
- float sum_level = 0, sum_power = 0;
+ float sum_level = 0;
 
  for (i = 0; i < nsamples; ++i) {
  I = *in++;
@@ -142,7 +158,6 @@ static void convert_uc8_generic(void *iq_data,
  magsq = 1;
 
  float mag = sqrtf(magsq);
- sum_power += magsq;
  sum_level += mag;
  *mag_data++ = (uint16_t)(mag * 65535.0f + 0.5f);
  }
@@ -155,7 +170,7 @@ static void convert_uc8_generic(void *iq_data,
  }
 
  if (out_mean_power) {
- *out_mean_power = sum_power / nsamples;
+ *out_mean_power = *out_mean_level * *out_mean_level;
  }
 }
 
@@ -175,7 +190,7 @@ static void convert_sc16_generic(void *iq_data,
  unsigned i;
  int16_t I, Q;
  float fI, fQ, magsq;
- float sum_level = 0, sum_power = 0;
+ float sum_level = 0;
 
  for (i = 0; i < nsamples; ++i) {
  I = (int16_t)le16toh(*in++);
@@ -194,7 +209,6 @@ static void convert_sc16_generic(void *iq_data,
  magsq = 1;
 
  float mag = sqrtf(magsq);
- sum_power += magsq;
  sum_level += mag;
  *mag_data++ = (uint16_t)(mag * 65535.0f + 0.5f);
  }
@@ -207,7 +221,7 @@ static void convert_sc16_generic(void *iq_data,
  }
 
  if (out_mean_power) {
- *out_mean_power = sum_power / nsamples;
+ *out_mean_power = *out_mean_level * *out_mean_level;
  }
 }
 
@@ -225,7 +239,7 @@ static void convert_sc16_nodc(void *iq_data,
  unsigned i;
  int16_t I, Q;
  float fI, fQ, magsq;
- float sum_level = 0, sum_power = 0;
+ float sum_level = 0;
 
  for (i = 0; i < nsamples; ++i) {
  I = (int16_t)le16toh(*in++);
@@ -238,7 +252,6 @@ static void convert_sc16_nodc(void *iq_data,
  magsq = 1;
 
  float mag = sqrtf(magsq);
- sum_power += magsq;
  sum_level += mag;
  *mag_data++ = (uint16_t)(mag * 65535.0f + 0.5f);
  }
@@ -248,7 +261,7 @@ static void convert_sc16_nodc(void *iq_data,
  }
 
  if (out_mean_power) {
- *out_mean_power = sum_power / nsamples;
+ *out_mean_power = *out_mean_level * *out_mean_level;
  }
 }
 
@@ -305,7 +318,6 @@ static void convert_sc16q11_table(void *iq_data,
  unsigned i;
  uint16_t I, Q;
  uint64_t sum_level = 0;
- uint64_t sum_power = 0;
  uint16_t mag;
 
  MODES_NOTUSED(state);
@@ -316,15 +328,14 @@ static void convert_sc16q11_table(void *iq_data,
  mag = sc16q11_lookup[((I >> LOSE_BITS) << USE_BITS) | (Q >> LOSE_BITS)];
  *mag_data++ = mag;
  sum_level += mag;
- sum_power += (uint32_t)mag * (uint32_t)mag;
  }
 
  if (out_mean_level) {
  *out_mean_level = sum_level / 65536.0 / nsamples;
  }
 
  if (out_mean_power) {
- *out_mean_power = sum_power / 65535.0 / 65535.0 / nsamples;
+ *out_mean_power = *out_mean_level * *out_mean_level;
  }
 }
 
@@ -344,7 +355,7 @@ static void convert_sc16q11_nodc(void *iq_data,
  unsigned i;
  int16_t I, Q;
  float fI, fQ, magsq;
- float sum_level = 0, sum_power = 0;
+ float sum_level = 0;
 
  for (i = 0; i < nsamples; ++i) {
  I = (int16_t)le16toh(*in++);
@@ -357,7 +368,6 @@ static void convert_sc16q11_nodc(void *iq_data,
  magsq = 1;
 
  float mag = sqrtf(magsq);
- sum_power += magsq;
  sum_level += mag;
  *mag_data++ = (uint16_t)(mag * 65535.0f + 0.5f);
  }
@@ -367,7 +377,7 @@ static void convert_sc16q11_nodc(void *iq_data,
  }
 
  if (out_mean_power) {
- *out_mean_power = sum_power / nsamples;
+ *out_mean_power = *out_mean_level * *out_mean_level;
  }
 }
 
@@ -389,7 +399,7 @@ static void convert_sc16q11_generic(void *iq_data,
  unsigned i;
  int16_t I, Q;
  float fI, fQ, magsq;
- float sum_level = 0, sum_power = 0;
+ float sum_level = 0;
 
  for (i = 0; i < nsamples; ++i) {
  I = (int16_t)le16toh(*in++);
@@ -408,7 +418,6 @@ static void convert_sc16q11_generic(void *iq_data,
  magsq = 1;
 
  float mag = sqrtf(magsq);
- sum_power += magsq;
  sum_level += mag;
  *mag_data++ = (uint16_t)(mag * 65535.0f + 0.5f);
  }
@@ -421,7 +430,7 @@ static void convert_sc16q11_generic(void *iq_data,
  }
 
  if (out_mean_power) {
- *out_mean_power = sum_power / nsamples;
+ *out_mean_power = *out_mean_level * *out_mean_level;
  }
 }