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/*
* divsf3.s
*
* Floating point divide, single precision: r0r1 /= r2r3
*
* The contents of this file are subject to the Mozilla Public License
* Version 1.0 (the "License"); you may not use this file except in
* compliance with the License. You may obtain a copy of the License at
* http://www.mozilla.org/MPL/
*
* Software distributed under the License is distributed on an "AS IS"
* basis, WITHOUT WARRANTY OF ANY KIND, either express or implied. See the
* License for the specific language governing rights and limitations
* under the License.
*
* The Original Code is Librcx floating point code, released May 27, 1999.
*
* The Initial Developer of the Original Code is Kekoa Proudfoot.
* Portions created by Kekoa Proudfoot are Copyright (C) 1999
* Kekoa Proudfoot. All Rights Reserved.
*
* Contributor(s): Kekoa Proudfoot <kekoa@graphics.stanford.edu>
*
* Includes bug fixes by Evgeni Krimer <krimer at tx.technion.ac.il>
* and Roman Barsky <barsky at cs.technion.ac.il>
* Project site - http://www.cs.technion.ac.il/~barsky/brickos.html
* Last updated 26 Oct 2003
*
*/
.section .text
;;
;; function: divsf3
;; input: float in r0r1 and float at sp+2
;; output: float in r0r1
;;
.global ___divsf3
___divsf3:
; Invoke the preamble to expand input operands
jsr ___startsf
; At this point, registers/stack contain the following:
; r0r1 - first operand
; r2h - second operand flags
; r2l - second operand sign
; r3h - first operand flags
; r3l - first operand sign
; r4 - first operand exponent
; r5r6 - first operand mantissa
; sp+0 - second operand exponent
; sp+2 - second operand flags (same as r2h)
; sp+3 - second operand sign (same as r2l)
; sp+4 - second operand mantissa
; sp+16 - second operand
; Note on flag bits: 0=zero, 1=inf, 2=nan
; Is the first operand a NaN?
; If yes, return the first operand (the value already in r0r1)
bld #2,r3h ; if nan flag of first operand set
; Hack!
bcs return_jmp ; carry set indicates true
; Is the second operand a NaN?
bld #2,r2h ; if nan flag of second operand set
bcc endif_0 ; carry clear indicates false
; Return the second operand (which we need to load off stack)
mov.w @(16,r7),r0 ; set return value to second operand (sp+16)
mov.w @(18,r7),r1
; Hack!
bra return_jmp
endif_0:
; Are both operands zero or both operands infinity?
bld #0,r3h ; load zero flag of first operand to carry
band #0,r2h ; and carry with zero flag of second operand
bcs if_1 ; carry set indicates true
bld #1,r3h ; load inf flag of first operand to carry
band #1,r2h ; and carry with inf flag of second operand
bcc endif_1 ; carry clear indicates false
if_1:
; Zero divided by zero or infinity divided by infinity, so return NaN
mov.w #0x7fff,r0 ; set return value to NaN (7fffffff)
mov.w #0xffff,r1
; Hack!
return_jmp:
bra return
endif_1:
; Compute new sign byte
xor.b r2l,r3l ; xor second sign (r2l) into first sign (r3l)
; At this point, we no longer need the following:
; r0r1 - first operand
; r2h - second operand flags
; r2l - second operand sign
; r3h - first operand flags
; Is second operand zero or first operand infinity?
bld #0,r2h ; load zero flag of second operand to carry
bor #1,r3h ; or carry with inf flag of first operand
bcc endif_2
; Return +/- infinity according to sign
mov.w #0x7f80,r0 ; load infinity (7f800000) to return value
sub.w r1,r1
or.b r3l,r0h ; or sign bit into upper byte
bra return
endif_2:
; Compute new exponent
mov.w @r7,r0 ; load second operand exponend (sp+0) to temp
sub.w r0,r4 ; add temp to exponent of first operand (r4)
add.b #126,r4l ; add bias minus one (compensate for 2.29)
addx.b #0,r4h ; finish addition
; At this point r0 r1 r2 r3h are free and we want to perform a divide
; We need 6 words plus 1 byte of registers to do this
; Keep r3l where it is, but make r4 free
; Save result exponent to stack
mov.w r4,@r7 ; sp+0 is result exponent
; Numerator (first operand mantissa) already in r5r6
; Load denominator (second operand mantissa) to r0r1
mov.w @(4,r7),r0 ; sp+4 is second operand mantissa
mov.w @(6,r7),r1
; Initialize quotient (r2r4)
sub.w r2,r2 ; load zero to r2r4
sub.w r4,r4
; Initialize counter (r3h)
mov.b #26,r3h ; set counter to 26
; Divide
dowhile_3:
; If numerator >= denominator
cmp.w r0,r5 ; compare upper words (r5 ? r0)
;bgt if_4 ; greater than indicates true
; NOTE that previous line compares
; signed which causes a bug
; fixed by Krimer and Barsky
bhi if_4 ; greater than indicates true
;blt endif_4 ; less than indicates false
; NOTE that previous line compares
; signed which causes a bug
; fixed by Krimer and Barsky
blo endif_4 ; less than indicates false
cmp.w r1,r6 ; compare lower words (r6 ? r1)
;blt endif_4 ; less than indicates false
; NOTE that previous line compares
; signed which causes a bug
; fixed by Krimer and Barsky
blo endif_4 ; less than indicates false
if_4:
; Subtract denominator from numerator
sub.w r1,r6 ; subtract r0r1 from r5r6
subx.b r0l,r5l
subx.b r0h,r5h
; Set quotient bit
bset #4,r4l ; set 1 << 4 bit of quotient
endif_4:
; Shift numerator and quotient left one place
add.w r6,r6 ; shift numerator left one place using add
addx.b r5l,r5l
addx.b r5h,r5h
add.w r4,r4 ; shift quotient left one place using add
addx.b r2l,r2l
addx.b r2h,r2h
; Decrement counter
dec.b r3h ; decrement counter
bne dowhile_3 ; repeat if counter not yet zero
; Set sticky bit of quotient if remainder (numerator) is non-zero
or.b r5h,r5l ; or remainder bytes together
or.b r5l,r6h
or.b r6h,r6l
add.b #0xff,r6l ; set carry if remainder non-zero
bst #0,r4l ; store sticky bit (carry) in lsb of quotient
; Move result to r5r6
mov.w r2,r5 ; copy quotient to r5r6
mov.w r4,r6
; Restore result exponent from stack
mov.w @r7,r4 ; sp+0 is result exponent
; Join
jsr ___joinsf
return:
; Invoke the epilogue to cleanup and return
jmp ___finishsf
|
