Initial revision

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Initial revision

1 files changed, 102 insertions, 0 deletions

diff --git a/gst/law/mulaw-conversion.c b/gst/law/mulaw-conversion.c
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+/*
+ * This routine converts from linear to ulaw
+ * 29 September 1989
+ *
+ * Craig Reese: IDA/Supercomputing Research Center
+ * Joe Campbell: Department of Defense
+ *
+ * References:
+ * 1) CCITT Recommendation G.711  (very difficult to follow)
+ * 2) "A New Digital Technique for Implementation of Any 
+ *     Continuous PCM Companding Law," Villeret, Michel,
+ *     et al. 1973 IEEE Int. Conf. on Communications, Vol 1,
+ *     1973, pg. 11.12-11.17
+ * 3) MIL-STD-188-113,"Interoperability and Performance Standards
+ *     for Analog-to_Digital Conversion Techniques,"
+ *     17 February 1987
+ *
+ * Input: Signed 16 bit linear sample
+ * Output: 8 bit ulaw sample
+ */
+
+#include <glib.h>
+
+#define ZEROTRAP    /* turn on the trap as per the MIL-STD */
+#define BIAS 0x84   /* define the add-in bias for 16 bit samples */
+#define CLIP 32635
+
+void
+mulaw_encode(gint16* in, guint8* out, gint numsamples)
+{
+    static gint16 exp_lut[256] = {0,0,1,1,2,2,2,2,3,3,3,3,3,3,3,3,
+                               4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,4,
+                               5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,
+                               5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,5,
+                               6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,
+                               6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,
+                               6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,
+                               6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,6,
+                               7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
+                               7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
+                               7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
+                               7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
+                               7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
+                               7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
+                               7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,
+                               7,7,7,7,7,7,7,7,7,7,7,7,7,7,7,7};
+    gint16 sign, exponent, mantissa,i;
+    gint16 sample;
+    guint8 ulawbyte;
+
+    for(i=0;i<numsamples;i++) {
+      sample=in[i];
+      /** get the sample into sign-magnitude **/
+      sign = (sample >> 8) & 0x80;        /* set aside the sign */
+      if (sign != 0) sample = -sample;    /* get magnitude */
+      if (sample > CLIP) sample = CLIP;   /* clip the magnitude */
+      /** convert from 16 bit linear to ulaw **/
+      sample = sample + BIAS;
+      exponent = exp_lut[(sample>>7) & 0xFF];
+      mantissa = (sample >> (exponent+3)) & 0x0F;
+      ulawbyte = ~(sign | (exponent << 4) | mantissa);
+#ifdef ZEROTRAP
+      if (ulawbyte == 0 ) ulawbyte = 0x02;  /* optional CCITT trap */
+#endif
+      out[i]=ulawbyte;
+    }
+}
+
+/*
+ * This routine converts from ulaw to 16 bit linear
+ * 29 September 1989
+ *
+ * Craig Reese: IDA/Supercomputing Research Center
+ *
+ * References:
+ * 1) CCITT Recommendation G.711  (very difficult to follow)
+ * 2) MIL-STD-188-113,"Interoperability and Performance Standards
+ *     for Analog-to_Digital Conversion Techniques,"
+ *     17 February 1987
+ *
+ * Input: 8 bit ulaw sample
+ * Output: signed 16 bit linear sample
+ */
+
+void
+mulaw_decode(guint8* in,gint16* out,gint numsamples)
+{
+    static gint16 exp_lut[8]={0,132,396,924,1980,4092,8316,16764};
+    gint16 sign, exponent, mantissa;
+    guint8 ulawbyte;
+    gint16 linear,i;
+    for(i=0;i<numsamples;i++) {
+      ulawbyte=in[i];
+      ulawbyte = ~ulawbyte;
+      sign = (ulawbyte & 0x80);
+      exponent = (ulawbyte >> 4) & 0x07;
+      mantissa = ulawbyte & 0x0F;
+      linear = exp_lut[exponent] + (mantissa << (exponent+3));
+      if (sign != 0) linear = -linear;
+      out[i]=linear;
+    }
+}