log2_norm.asm

基于TMS320F2812的AMR+RS编解码+OFDM调制解调源程序。是stand alone运行版本

*****************************************************************************
** Description:     log2_norm() in log2.c                              **
**                                                                         **
** Inputs                                                                  **
**                                                                         **
**   xar0---Word32 L_x                                                     **
**   ar1 ---Word16 exp                                                     **  
** Outputs:                                                                **
**   ar2 ---word16 *exponent                                              **
**   ar3 ---word16 *fraction                                              **
**                                                                         **
**                                                                         **
** Return value :                                                     	   **
**                                                                         **
** Attribute    :       Cycles: 100       Pm: 57                          **
**                      Modified Registers:  all                           **
**                                                                         **
** Programmer   :       xiewei                                     **
*****************************************************************************

  .ref    log_table
  .global _log2_norm
_log2_norm: 

	movl acc,@XAR0        ; if (L_x <= (Word32) 0)
	;movl xar2,#0
	;movl xar3,#2
	sb _line_33,GT      ;*exponent = 0;           
        				;*fraction = 0; 
	mov ar2,#0   
	mov ar3,#0
    LRETR  
_line_33:
    MOV AL,#30       ;*exponent = sub (30, exp);
	SUB AL,@ar1
	MOV ar2,al
	MOVL ACC,@XAR0
	MOVL @XAR4,ACC
	MOV T,#9
	ASRL ACC,T
	MOVL @XAR0,ACC
	MOVL ACC,@XAR4
	SB _line_49,GEQ
	NOT ACC
	MOV T,#9
	ASRL ACC,T
	NOT ACC
	MOVL @XAR0,ACC
_line_49: 	
    MOVL ACC,@XAR0
   	MOV @ar4,AH
   	MOVL @XAR5,ACC
	MOV T,#1
	ASRL ACC,T
	MOVL @XAR0,ACC
	MOVL ACC,@XAR4
	SB _line_63,GEQ   
	NOT ACC
	MOV T,#1
	ASRL ACC,T 
	NOT ACC
	MOVL @XAR0,ACC
_line_63:
 	MOVL ACC,@XAR0
 	AND AL,#0x7fff
 	MOV @AR5,AL
	MOV AL,@AR4
	SUB AL,#32
	MOV @AR4,AL
	MOVL XAR6,#log_table
	MOV AH,#0
 	ADDL @XAR6,ACC	
  	MOV AH,*XAR6++
 	MOV AL,#0
	MOVL @XAR7,ACC
	SUB AH,*XAR6
	MOV T,AH
	SPM 1		
	MPY P,T,@AR5
	MOVL ACC,@XAR7
	SUBL ACC,P<<PM
	MOV AR3,AH
    LRETR