alaw.h

DTMF检测程序

#define SIGN_BIT	(0x80)		/* Sign bit for a A-law byte. */
#define QUANT_MASK	(0xf)		/* Quantization field mask. */
#define NSEGS		(8)		/* Number of A-law segments. */
#define SEG_SHIFT	(4)		/* Left shift for segment number. */
#define SEG_MASK	(0x70)		/* Segment field mask. */

unsigned char linear2alaw(short pcm_val);
short alaw2linear(unsigned char a_val);