1 files changed, 85 insertions, 0 deletions
diff --git a/alaw.c b/alaw.c
new file mode 100755
index 000000000..d0495e5f6
--- /dev/null
+++ b/alaw.c
@@ -0,0 +1,85 @@
+/*
+ * Asterisk -- A telephony toolkit for Linux.
+ *
+ * u-Law to Signed linear conversion
+ * 
+ * Copyright (C) 1999, Mark Spencer
+ *
+ * Mark Spencer <markster@linux-support.net>
+ *
+ * This program is free software, distributed under the terms of
+ * the GNU General Public License
+ */
+
+#include <asterisk/alaw.h>
+
+#define AMI_MASK 0x55
+
+static inline unsigned char linear2alaw (short int linear)
+{
+    int mask;
+    int seg;
+    int pcm_val;
+    static int seg_end[8] =
+    {
+         0xFF, 0x1FF, 0x3FF, 0x7FF, 0xFFF, 0x1FFF, 0x3FFF, 0x7FFF
+    };
+    
+    pcm_val = linear;
+    if (pcm_val >= 0)
+    {
+        /* Sign (7th) bit = 1 */
+        mask = AMI_MASK | 0x80;
+    }
+    else
+    {
+        /* Sign bit = 0 */
+        mask = AMI_MASK;
+        pcm_val = -pcm_val;
+    }
+
+    /* Convert the scaled magnitude to segment number. */
+    for (seg = 0;  seg < 8;  seg++)
+    {
+        if (pcm_val <= seg_end[seg])
+	    break;
+    }
+    /* Combine the sign, segment, and quantization bits. */
+    return  ((seg << 4) | ((pcm_val >> ((seg)  ?  (seg + 3)  :  4)) & 0x0F)) ^ mask;
+}
+/*- End of function --------------------------------------------------------*/
+
+static inline short int alaw2linear (unsigned char alaw)
+{
+    int i;
+    int seg;
+
+    alaw ^= AMI_MASK;
+    i = ((alaw & 0x0F) << 4);
+    seg = (((int) alaw & 0x70) >> 4);
+    if (seg)
+        i = (i + 0x100) << (seg - 1);
+    return (short int) ((alaw & 0x80)  ?  i  :  -i);
+}
+
+unsigned char __ast_lin2a[8192];
+short __ast_alaw[256];
+
+void ast_alaw_init(void)
+{
+	int i;
+	/* 
+	 *  Set up mu-law conversion table
+	 */
+	for(i = 0;i < 256;i++)
+	   {
+	        __ast_alaw[i] = alaw2linear(i);
+	   }
+	  /* set up the reverse (mu-law) conversion table */
+	for(i = -32768; i < 32768; i++)
+	   {
+		__ast_lin2a[((unsigned short)i) >> 3] = linear2alaw(i);
+	   }
+
+}
+