divides two unsigned 32 bit values and returns their quotient and remainder.txt

c6000的应用程序比较常用比如说fft ifft等一些原文件

*TEXAS INSTRUMENTS, INC.		
*
*	DIVMODU32
*
*	Revision Date:  07/15/97
*	
*	USAGE	This routine is C Callable and can be called as:
*
*		struct	divmodu divmodu32(unsigned int a, unsigned int b);
*		
*		a --- unsigned numerator 
*               b --- unsigned denominator
*
*		If routine is not to be used as a C callable function then
*		you need to initialize values for all of the values passed
*		as these are assumed to be in registers as defined by the 
*		calling convention of the compiler, (refer to the C compiler
*		reference guide).
*
*	C CODE
*		This is the C equivalent of the assembly code.  Note that
*		the assembly code is hand optimized and restrictions may
*		apply.
*
*
*		struct	divmodu {
*			unsigned int div;
*			unsigned int mod;
*		};
*
*
*		struct divmodu divmodu32(unsigned int a, unsigned int b)
*		{
*		        struct divmodu tmp;
*		
*			tmp.div = a / b;
*			tmp.mod = a % b;
*
*			return tmp;
*		}
*
*	DESCRIPTION
*
*		This routine divides two unsigned 32 bit values and returns
*		their quotient and remainder.  The inputs are unsigned 32-bit
*		numbers, and the result is a unsigned 32-bit number.
*
*	TECHNIQUE
*		
*		The loop is executed at least 6 times.  In the loop, the
*		conditional subtract divide step (SUBC) is block from doing
*		extraneous executions.  In short, the SUBC instruction
*		is conditional and will not necessarily be executed.
*
*	MEMORY NOTE
*	
*		No memory bank hits under any conditions.		
*
*	CYCLES
*
*		Minimum execution time -> 18 cycles
*		Maximum	execution time -> 42 cycles
*
*==============================================================================

	.global _divmodu32
	.text

_divmodu32:

*** BEGIN Benchmark Timing ***
B_START:
	LMBD	.L2X	1,	A4,	B1	; mag_num = lmbd(1, num)
||	LMBD	.L1X	1,	B4,	A1	; mag_den = lmbd(1, den)
||	MVK	.S1	32,	A0		; const 32
||	ZERO	.D1	A8			; first_div = 1

	CMPGTU	.L1X	B4,	A4,	A1	; zero = (den > num)
||	SUB	.L2X	A1,	B1,	B0	; i = mag_den - mag_num
||	MV	.D1	A4,	A5		; save num
||[!B1]	MVK	.S1	1,	A8		; if (num32) first_div = 1

	SHL	.S2	B4,	B0,	B4	; den <<= i
||[B1]	ADD	.D2	B0,	1,	B0	; if (!num32) i++
||	MV		B0,	A6

	CMPGTU	.L2X	B4,	A4,	B2	; gt = den > num
||	SUB	.L1X	A0,	B0,	A0	; qs = 32 - i
||	SHL	.S1	A8,	A6,	A8	; first_div <<= i
||	B	.S2	LOOP			;
||[B1]	MPY	.M2	B2,	0,	B2	; num32 && gt

	ADD	.L1X	0,	B0,	A2
||[B2]	MV	.D2	B2,	B1		; !(num32 && !gt)
||[B2]	SHRU	.S1	A8,	1,	A8	; first_div >>= 1
||	B	.S2	LOOP			;

  [B2]	SHRU	.S2	B4,	1,	B4	; if (num32 && gt) den >> 1
||[!B1]	SUB	.L1X	A4,	B4,	A4	; if (num32 && !gt) num -= den
||[B0]	SUB	.D2	B0,	1,	B0	; i--
||	B	.S1	LOOP			;

  [!B1]	SHRU	.S2	B4,	1,	B4	; if (num32 && !gt) den >> 1
||[B2]	SUB	.L1X	A4,	B4,	A4	; if (num32 && gt) num -= den
||	CMPLT	.L2	B0,	6,	B2	; check for neg. loop counter
||	SUB	.D2	B0,	6,	B1	; generate loop counter
||	B	.S1	LOOP			;

  [B2]	ZERO	.L2	B1			; zero negative loop counter
||[A2]	SUBC	.L1X	A4,	B4,	A4	; num = subc(num, den)
||	B	.S2	LOOP			;

LOOP:
  [B0]	SUBC	.L1X	A4,	B4,	A4	; num = subc(num, den)
||[B0]	SUB	.L2	B0,	1,	B0	; i--
||[B1]	SUB	.D2	B1,	1,	B1	; i--
||[B1]	B	.S1	LOOP			; for

;end of LOOP

  	ADD	.L2	A3,	4,	B7	; address for mod result
||[!A1]	SHL	.S1	A4,	A0,	A6	; q = num << qs
||[A1]	MPY	.M1	0,	A6,	A6	; if (zero) q = zero
||	B	.S2	B3	

  [!A1]	SHRU	.S1	A6,	A0,	A6	; q = num >> qs
||[A1]	MV	.L1	A5,	A2		; if (zero) mod = num
||	MV		A8,	B5		;

	ADD	.L2X	A6,	B5,	B8	;
||[!A1]	SHRU	.S1	A4,	A2,	A2	; mod = n >> ms

	STW	.D1	B8,	*A3++		; c[2 * i] = q
||	STW	.D2	A2,	*B7++		; c[2 * i + 1] = mod

B_END:
*** END Benchmark Timing ***

	NOP	2