1000bytes RAM saved

radio/util/codecs.py

@@ -0,0 +1,51 @@
+#!/bin/env python
+
+SIGN_BIT =       (0x80)      # Sign bit for a A-law byte.
+QUANT_MASK =     (0xf)       # Quantization field mask.
+SEG_SHIFT =      (4)         # Left shift for segment number.
+SEG_MASK =       (0x70)      # Segment field mask.
+BIAS =           (0x84)      # Bias for linear code.
+
+def alaw2linear(a_val):
+    a_val ^= 0x55
+    
+    t = a_val & QUANT_MASK
+    seg = (a_val & SEG_MASK) >> SEG_SHIFT
+    if (seg):
+        t = (t + t + 1 + 32) << (seg + 2)
+    else:
+        t = (t + t + 1     ) << 3
+    
+    if a_val & SIGN_BIT:
+        return t
+    else:
+        return -t
+
+def ulaw2linear(u_val):   
+    # Complement to obtain normal u-law value.
+    u_val = ~u_val
+    
+    # Extract and bias the quantization bits. Then
+    # shift up by the segment number and subtract out the bias.
+    t = ((u_val & QUANT_MASK) << 3) + BIAS
+    t <<= (u_val & SEG_MASK) >> SEG_SHIFT
+    
+    if u_val & SIGN_BIT:
+        return (BIAS - t)
+    else:
+        return (t - BIAS)
+
+def pcmTable(fn):
+    result = []
+    for i in range(256):
+        result.append(fn(i))
+    return result
+
+def tableToString(name, table):   
+    result =  'const int16_t ' + name + '[256] = { ' 
+    result += ', '.join([str(i) for i in table])
+    result += ' };'
+    return result
+    
+print tableToString('alawTable', pcmTable(alaw2linear))
+print tableToString('ulawTable', pcmTable(ulaw2linear))