Refactoring vad_gmm.[c/h].

- Changed to stdint.
- Replaced SHIFT macros.
- Variable name changes.
- Style changes.
- Comments updates.
- Added a unit test.
Review URL: http://webrtc-codereview.appspot.com/323011

git-svn-id: http://webrtc.googlecode.com/svn/trunk@1249 4adac7df-926f-26a2-2b94-8c16560cd09d

src/common_audio/vad/vad_gmm.c

@@ -8,68 +8,76 @@
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
-
-/*
- * This file includes the implementation of the internal VAD call
- * WebRtcVad_GaussianProbability. For function description, see vad_gmm.h.
- */
-
 #include "vad_gmm.h"
 
 #include "signal_processing_library.h"
 #include "typedefs.h"
 
-static const WebRtc_Word32 kCompVar = 22005;
+static const int32_t kCompVar = 22005;
-// Constant log2(exp(1)) in Q12
+static const int16_t kLog2Exp = 5909;  // log2(exp(1)) in Q12.
-static const WebRtc_Word16 kLog10Const = 5909;
 
-WebRtc_Word32 WebRtcVad_GaussianProbability(WebRtc_Word16 in_sample,
+// For a normal distribution, the probability of |input| is calculated and
-                                            WebRtc_Word16 mean,
+// returned (in Q20). The formula for normal distributed probability is
-                                            WebRtc_Word16 std,
+//
-                                            WebRtc_Word16 *delta)
+// 1 / s * exp(-(x - m)^2 / (2 * s^2))
-{
+//
-    WebRtc_Word16 tmp16, tmpDiv, tmpDiv2, expVal, tmp16_1, tmp16_2;
+// where the parameters are given in the following Q domains:
-    WebRtc_Word32 tmp32, y32;
+// m = |mean| (Q7)
+// s = |std| (Q7)
+// x = |input| (Q4)
+// in addition to the probability we output |delta| (in Q11) used when updating
+// the noise/speech model.
+int32_t WebRtcVad_GaussianProbability(int16_t input,
+                                      int16_t mean,
+                                      int16_t std,
+                                      int16_t* delta) {
+  int16_t tmp16, inv_std, inv_std2, exp_value = 0;
+  int32_t tmp32;
 
-    // Calculate tmpDiv=1/std, in Q10
+  // Calculate |inv_std| = 1 / s, in Q10.
-    tmp32 = (WebRtc_Word32)WEBRTC_SPL_RSHIFT_W16(std,1) + (WebRtc_Word32)131072; // 1 in Q17
+  // 131072 = 1 in Q17, and (|std| >> 1) is for rounding instead of truncation.
-    tmpDiv = (WebRtc_Word16)WebRtcSpl_DivW32W16(tmp32, std); // Q17/Q7 = Q10
+  // Q-domain: Q17 / Q7 = Q10.
+  tmp32 = (int32_t) 131072 + (int32_t) (std >> 1);
+  inv_std = (int16_t) WebRtcSpl_DivW32W16(tmp32, std);
 
-    // Calculate tmpDiv2=1/std^2, in Q14
+  // Calculate |inv_std2| = 1 / s^2, in Q14.
-    tmp16 = WEBRTC_SPL_RSHIFT_W16(tmpDiv, 2); // From Q10 to Q8
+  tmp16 = (inv_std >> 2);  // Q10 -> Q8.
-    tmpDiv2 = (WebRtc_Word16)WEBRTC_SPL_MUL_16_16_RSFT(tmp16, tmp16, 2); // (Q8 * Q8)>>2 = Q14
+  // Q-domain: (Q8 * Q8) >> 2 = Q14.
+  inv_std2 = (int16_t) WEBRTC_SPL_MUL_16_16_RSFT(tmp16, tmp16, 2);
+  // TODO(bjornv): Investigate if changing to
+  // |inv_std2| = (int16_t) WEBRTC_SPL_MUL_16_16_RSFT(|inv_std|, |inv_std|, 6);
+  // gives better accuracy.
 
-    tmp16 = WEBRTC_SPL_LSHIFT_W16(in_sample, 3); // Q7
+  tmp16 = (input << 3);  // Q4 -> Q7
   tmp16 = tmp16 - mean;  // Q7 - Q7 = Q7
 
-    // To be used later, when updating noise/speech model
+  // To be used later, when updating noise/speech model.
-    // delta = (x-m)/std^2, in Q11
+  // |delta| = (x - m) / s^2, in Q11.
-    *delta = (WebRtc_Word16)WEBRTC_SPL_MUL_16_16_RSFT(tmpDiv2, tmp16, 10); //(Q14*Q7)>>10 = Q11
+  // Q-domain: (Q14 * Q7) >> 10 = Q11.
+  *delta = (int16_t) WEBRTC_SPL_MUL_16_16_RSFT(inv_std2, tmp16, 10);
 
-    // Calculate tmp32=(x-m)^2/(2*std^2), in Q10
+  // Calculate the exponent |tmp32| = (x - m)^2 / (2 * s^2), in Q10. Replacing
-    tmp32 = (WebRtc_Word32)WEBRTC_SPL_MUL_16_16_RSFT(*delta, tmp16, 9); // One shift for /2
+  // division by two with one shift.
+  // Q-domain: (Q11 * Q7) >> 8 = Q10.
+  tmp32 = WEBRTC_SPL_MUL_16_16_RSFT(*delta, tmp16, 9);
 
-    // Calculate expVal ~= exp(-(x-m)^2/(2*std^2)) ~= exp2(-log2(exp(1))*tmp32)
+  // If the exponent is small enough to give a non-zero probability we calculate
-    if (tmp32 < kCompVar)
+  // |exp_value| ~= exp(-(x - m)^2 / (2 * s^2))
-    {
+  //             ~= exp2(-log2(exp(1)) * |tmp32|).
-        // Calculate tmp16 = log2(exp(1))*tmp32 , in Q10
+  if (tmp32 < kCompVar) {
-        tmp16 = (WebRtc_Word16)WEBRTC_SPL_MUL_16_16_RSFT((WebRtc_Word16)tmp32,
+    // Calculate |tmp16| = log2(exp(1)) * |tmp32|, in Q10.
-                                                         kLog10Const, 12);
+    // Q-domain: (Q12 * Q10) >> 12 = Q10.
+    tmp16 = (int16_t) WEBRTC_SPL_MUL_16_16_RSFT(kLog2Exp, (int16_t) tmp32, 12);
     tmp16 = -tmp16;
-        tmp16_2 = (WebRtc_Word16)(0x0400 | (tmp16 & 0x03FF));
+    exp_value = (0x0400 | (tmp16 & 0x03FF));
-        tmp16_1 = (WebRtc_Word16)(tmp16 ^ 0xFFFF);
+    tmp16 ^= 0xFFFF;
-        tmp16 = (WebRtc_Word16)WEBRTC_SPL_RSHIFT_W16(tmp16_1, 10);
+    tmp16 >>= 10;
     tmp16 += 1;
-        // Calculate expVal=log2(-tmp32), in Q10
+    // Get |exp_value| = exp(-|tmp32|) in Q10.
-        expVal = (WebRtc_Word16)WEBRTC_SPL_RSHIFT_W32((WebRtc_Word32)tmp16_2, tmp16);
+    exp_value >>= tmp16;
-
-    } else
-    {
-        expVal = 0;
   }
 
-    // Calculate y32=(1/std)*exp(-(x-m)^2/(2*std^2)), in Q20
+  // Calculate and return (1 / s) * exp(-(x - m)^2 / (2 * s^2)), in Q20.
-    y32 = WEBRTC_SPL_MUL_16_16(tmpDiv, expVal); // Q10 * Q10 = Q20
+  // Q-domain: Q10 * Q10 = Q20.
-
+  return WEBRTC_SPL_MUL_16_16(inv_std, exp_value);
-    return y32; // Q20
 }

src/common_audio/vad/vad_gmm.h

@@ -8,40 +8,32 @@
  *  be found in the AUTHORS file in the root of the source tree.
  */
 
+// Gaussian probability calculations internally used in vad_core.c.
 
-/*
+#ifndef WEBRTC_COMMON_AUDIO_VAD_VAD_GMM_H_
- * This header file includes the description of the internal VAD call
+#define WEBRTC_COMMON_AUDIO_VAD_VAD_GMM_H_
- * WebRtcVad_GaussianProbability.
- */
-
-#ifndef WEBRTC_VAD_GMM_H_
-#define WEBRTC_VAD_GMM_H_
 
 #include "typedefs.h"
 
-/****************************************************************************
+// Calculates the probability for |input|, given that |input| comes from a
- * WebRtcVad_GaussianProbability(...)
+// normal distribution with mean and standard deviation (|mean|, |std|).
- *
+//
- * This function calculates the probability for the value 'in_sample', given that in_sample
+// Inputs:
- * comes from a normal distribution with mean 'mean' and standard deviation 'std'.
+//      - input         : input sample in Q4.
- *
+//      - mean          : mean input in the statistical model, Q7.
- * Input:
+//      - std           : standard deviation, Q7.
- *      - in_sample     : Input sample in Q4
+//
- *      - mean          : mean value in the statistical model, Q7
+// Output:
- *      - std           : standard deviation, Q7
+//
- *
+//      - delta         : input used when updating the model, Q11.
- * Output:
+//                        |delta| = (|input| - |mean|) / |std|^2.
- *
+//
- *      - delta         : Value used when updating the model, Q11
+// Return:
- *
+//   (probability for |input|) =
- * Return:
+//    1 / |std| * exp(-(|input| - |mean|)^2 / (2 * |std|^2));
- *      - out           : out = 1/std * exp(-(x-m)^2/(2*std^2));
+int32_t WebRtcVad_GaussianProbability(int16_t input,
- *                        Probability for x.
+                                      int16_t mean,
- *
+                                      int16_t std,
- */
+                                      int16_t* delta);
-WebRtc_Word32 WebRtcVad_GaussianProbability(WebRtc_Word16 in_sample,
-                                            WebRtc_Word16 mean,
-                                            WebRtc_Word16 std,
-                                            WebRtc_Word16 *delta);
 
-#endif // WEBRTC_VAD_GMM_H_
+#endif  // WEBRTC_COMMON_AUDIO_VAD_VAD_GMM_H_

src/common_audio/vad/vad_unittest.cc

@@ -15,6 +15,13 @@
 #include "typedefs.h"
 #include "webrtc_vad.h"
 
+#ifdef __cplusplus
+extern "C"
+{
+#include "vad_gmm.h"
+}
+#endif
+
 namespace webrtc {
 namespace {
 const int16_t kModes[] = { 0, 1, 2, 3 };
@@ -152,6 +159,29 @@ TEST_F(VadTest, ApiTest) {
   EXPECT_EQ(0, WebRtcVad_Free(handle));
 }
 
+TEST_F(VadTest, GMMTests) {
+  int16_t delta = 0;
+  // Input value at mean.
+  EXPECT_EQ(1048576, WebRtcVad_GaussianProbability(0, 0, 128, &delta));
+  EXPECT_EQ(0, delta);
+  EXPECT_EQ(1048576, WebRtcVad_GaussianProbability(16, 128, 128, &delta));
+  EXPECT_EQ(0, delta);
+  EXPECT_EQ(1048576, WebRtcVad_GaussianProbability(-16, -128, 128, &delta));
+  EXPECT_EQ(0, delta);
+
+  // Largest possible input to give non-zero probability.
+  EXPECT_EQ(1024, WebRtcVad_GaussianProbability(59, 0, 128, &delta));
+  EXPECT_EQ(7552, delta);
+  EXPECT_EQ(1024, WebRtcVad_GaussianProbability(75, 128, 128, &delta));
+  EXPECT_EQ(7552, delta);
+  EXPECT_EQ(1024, WebRtcVad_GaussianProbability(-75, -128, 128, &delta));
+  EXPECT_EQ(-7552, delta);
+
+  // Too large input, should give zero probability.
+  EXPECT_EQ(0, WebRtcVad_GaussianProbability(105, 0, 128, &delta));
+  EXPECT_EQ(13440, delta);
+}
+
 // TODO(bjornv): Add a process test, run on file.
 
 }  // namespace