binstr.s

RTEMS (Real-Time Executive for Multiprocessor Systems) is a free open source real-time operating sys

//
//      $Id: binstr.S,v 1.1 1998/12/14 23:15:19 joel Exp $
//
//	binstr.sa 3.3 12/19/90
//
//	Description: Converts a 64-bit binary integer to bcd.
//
//	Input: 64-bit binary integer in d2:d3, desired length (LEN) in
//          d0, and a  pointer to start in memory for bcd characters
//          in d0. (This pointer must point to byte 4 of the first
//          lword of the packed decimal memory string.)
//
//	Output:	LEN bcd digits representing the 64-bit integer.
//
//	Algorithm:
//		The 64-bit binary is assumed to have a decimal point before
//		bit 63.  The fraction is multiplied by 10 using a mul by 2
//		shift and a mul by 8 shift.  The bits shifted out of the
//		msb form a decimal digit.  This process is iterated until
//		LEN digits are formed.
//
//	A1. Init d7 to 1.  D7 is the byte digit counter, and if 1, the
//		digit formed will be assumed the least significant.  This is
//		to force the first byte formed to have a 0 in the upper 4 bits.
//
//	A2. Beginning of the loop:
//		Copy the fraction in d2:d3 to d4:d5.
//
//	A3. Multiply the fraction in d2:d3 by 8 using bit-field
//		extracts and shifts.  The three msbs from d2 will go into
//		d1.
//
//	A4. Multiply the fraction in d4:d5 by 2 using shifts.  The msb
//		will be collected by the carry.
//
//	A5. Add using the carry the 64-bit quantities in d2:d3 and d4:d5
//		into d2:d3.  D1 will contain the bcd digit formed.
//
//	A6. Test d7.  If zero, the digit formed is the ms digit.  If non-
//		zero, it is the ls digit.  Put the digit in its place in the
//		upper word of d0.  If it is the ls digit, write the word
//		from d0 to memory.
//
//	A7. Decrement d6 (LEN counter) and repeat the loop until zero.
//
//	Implementation Notes:
//
//	The registers are used as follows:
//
//		d0: LEN counter
//		d1: temp used to form the digit
//		d2: upper 32-bits of fraction for mul by 8
//		d3: lower 32-bits of fraction for mul by 8
//		d4: upper 32-bits of fraction for mul by 2
//		d5: lower 32-bits of fraction for mul by 2
//		d6: temp for bit-field extracts
//		d7: byte digit formation word;digit count {0,1}
//		a0: pointer into memory for packed bcd string formation
//

//		Copyright (C) Motorola, Inc. 1990
//			All Rights Reserved
//
//	THIS IS UNPUBLISHED PROPRIETARY SOURCE CODE OF MOTOROLA 
//	The copyright notice above does not evidence any  
//	actual or intended publication of such source code.

//BINSTR    idnt    2,1 | Motorola 040 Floating Point Software Package

	|section	8

#include "fpsp.defs"

	.global	binstr
binstr:
	moveml	%d0-%d7,-(%a7)
//
// A1: Init d7
//
	moveql	#1,%d7			//init d7 for second digit
	subql	#1,%d0			//for dbf d0 would have LEN+1 passes
//
// A2. Copy d2:d3 to d4:d5.  Start loop.
//
loop:
	movel	%d2,%d4			//copy the fraction before muls
	movel	%d3,%d5			//to d4:d5
//
// A3. Multiply d2:d3 by 8; extract msbs into d1.
//
	bfextu	%d2{#0:#3},%d1		//copy 3 msbs of d2 into d1
	asll	#3,%d2			//shift d2 left by 3 places
	bfextu	%d3{#0:#3},%d6		//copy 3 msbs of d3 into d6
	asll	#3,%d3			//shift d3 left by 3 places
	orl	%d6,%d2			//or in msbs from d3 into d2
//
// A4. Multiply d4:d5 by 2; add carry out to d1.
//
	asll	#1,%d5			//mul d5 by 2
	roxll	#1,%d4			//mul d4 by 2
	swap	%d6			//put 0 in d6 lower word
	addxw	%d6,%d1			//add in extend from mul by 2
//
// A5. Add mul by 8 to mul by 2.  D1 contains the digit formed.
//
	addl	%d5,%d3			//add lower 32 bits
	nop				//ERRATA ; FIX #13 (Rev. 1.2 6/6/90)
	addxl	%d4,%d2			//add with extend upper 32 bits
	nop				//ERRATA ; FIX #13 (Rev. 1.2 6/6/90)
	addxw	%d6,%d1			//add in extend from add to d1
	swap	%d6			//with d6 = 0; put 0 in upper word
//
// A6. Test d7 and branch.
//
	tstw	%d7			//if zero, store digit & to loop
	beqs	first_d			//if non-zero, form byte & write
sec_d:
	swap	%d7			//bring first digit to word d7b
	aslw	#4,%d7			//first digit in upper 4 bits d7b
	addw	%d1,%d7			//add in ls digit to d7b
	moveb	%d7,(%a0)+		//store d7b byte in memory
	swap	%d7			//put LEN counter in word d7a
	clrw	%d7			//set d7a to signal no digits done
	dbf	%d0,loop		//do loop some more!
	bras	end_bstr		//finished, so exit
first_d:
	swap	%d7			//put digit word in d7b
	movew	%d1,%d7			//put new digit in d7b
	swap	%d7			//put LEN counter in word d7a
	addqw	#1,%d7			//set d7a to signal first digit done
	dbf	%d0,loop		//do loop some more!
	swap	%d7			//put last digit in string
	lslw	#4,%d7			//move it to upper 4 bits
	moveb	%d7,(%a0)+		//store it in memory string
//
// Clean up and return with result in fp0.
//
end_bstr:
	moveml	(%a7)+,%d0-%d7
	rts
	|end