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00025 #include "asterisk.h"
00026
00027 ASTERISK_FILE_VERSION(__FILE__, "$Revision: 7221 $")
00028
00029 #include "asterisk/alaw.h"
00030
00031 #define AMI_MASK 0x55
00032
00033 static inline unsigned char linear2alaw (short int linear)
00034 {
00035 int mask;
00036 int seg;
00037 int pcm_val;
00038 static int seg_end[8] =
00039 {
00040 0xFF, 0x1FF, 0x3FF, 0x7FF, 0xFFF, 0x1FFF, 0x3FFF, 0x7FFF
00041 };
00042
00043 pcm_val = linear;
00044 if (pcm_val >= 0)
00045 {
00046
00047 mask = AMI_MASK | 0x80;
00048 }
00049 else
00050 {
00051
00052 mask = AMI_MASK;
00053 pcm_val = -pcm_val;
00054 }
00055
00056
00057 for (seg = 0; seg < 8; seg++)
00058 {
00059 if (pcm_val <= seg_end[seg])
00060 break;
00061 }
00062
00063 return ((seg << 4) | ((pcm_val >> ((seg) ? (seg + 3) : 4)) & 0x0F)) ^ mask;
00064 }
00065
00066
00067 static inline short int alaw2linear (unsigned char alaw)
00068 {
00069 int i;
00070 int seg;
00071
00072 alaw ^= AMI_MASK;
00073 i = ((alaw & 0x0F) << 4);
00074 seg = (((int) alaw & 0x70) >> 4);
00075 if (seg)
00076 i = (i + 0x100) << (seg - 1);
00077 return (short int) ((alaw & 0x80) ? i : -i);
00078 }
00079
00080 unsigned char __ast_lin2a[8192];
00081 short __ast_alaw[256];
00082
00083 void ast_alaw_init(void)
00084 {
00085 int i;
00086
00087
00088
00089 for(i = 0;i < 256;i++)
00090 {
00091 __ast_alaw[i] = alaw2linear(i);
00092 }
00093
00094 for(i = -32768; i < 32768; i++)
00095 {
00096 __ast_lin2a[((unsigned short)i) >> 3] = linear2alaw(i);
00097 }
00098
00099 }
00100