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/*
* floatsisf.s
*
* Signed long to floating point conversion, single precision:
* r0r1 = (float) long r0r1
* Unsigned long to floating point conversion, single precision:
* r0r1 = (float) unsigned long r0r1
*
* GCC does not directly invoke the unsigned long conversion function
* Instead, it wraps the signed long function with a good amount of extra code
* You can save space by calling the latter conversion function yourself
* If you want to use it, you should invoke it yourself, as a function
* The declaration is: extern float __ufloatsisf (unsigned long value);
*
* 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>
*/
; possible optimizations
; - integrate msb test and sticky shift with fixoverflow in joinsf
; - add a bor #7,r5h to see if four bit is set
; - factor out stickyshift function, rewrite fixoverflow in joinsf to call it
; - affects this, since we can then call stickyshift right
; - if ufloatsisf removed, msb test should set mantissa to 7fffffff
; - also, msb test should be moved earlier to inside negative input test
.section .text
;;
;; function: ufloatsisf
;; input: unsigned long in r0r1
;; output: float in r0r1
;;
.global ___ufloatsisf
___ufloatsisf:
; Save registers (assume r2 and r3 saved by caller)
push r4
push r5
mov.w r6,r2 ; we need r6 specifically, but do not need r2
; Jump into floatsisf
bra ufloatentry
;;
;; function: floatsisf
;; input: signed long in r0r1
;; output: float in r0r1
;;
.global ___floatsisf
___floatsisf:
; Save registers (assume r2 and r3 saved by caller)
push r4
push r5
mov.w r6,r2 ; we need r6 specifically, but do not need r2
; Is input negative?
btst #7,r0h ; is r0r1 < 0?
beq else_0 ; equal indicates false
; Set sign to negative
mov.b #0x80,r3l ; set sign (r3l) to 0x80 to indicate negative
; Store -input to mantissa
sub.w r5,r5 ; zero destination
sub.w r6,r6
sub.w r1,r6 ; subtract input
subx.b r0l,r5l
subx.b r0h,r5h
bra endif_0
else_0:
ufloatentry:
; Set sign to positive
sub.b r3l,r3l ; set sign (r3l) to zero to indicate positive
; Store input to mantissa
mov.w r0,r5 ; set mantissa
mov.w r1,r6
endif_0:
; Set exponent
mov.w #156,r4 ; set exponent to 29 + bias, bias is 127
; Is msb set?
btst #7,r5h ; is msb set?
beq else_1 ; zero indicates false
; Mantissa overflow, so shift right one place, maintaining sticky bit
shlr.b r5h ; shift mantissa right 1 place
rotxr.b r5l
rotxr.b r6h
rotxr.b r6l ; last shift places old sticky bit in carry
bor #0,r6l ; or lsb with old sticky bit
bst #0,r6l ; store new sticky bit
; Increase exponent
adds #1,r4 ; add one to exponent
bra endif_1
else_1:
; Is mantissa non-zero?
mov.w r5,r5 ; check upper word
bne if_2 ; not equal to zero indicates true
mov.w r6,r6 ; check lower word
beq endif_2 ; equal to zero indicates false
if_2:
; Is the two bit (40000000) clear?
btst #6,r5h ; check 40000000 bit
bne endif_3 ; non-zero indicates false (bit set)
; Normalize
jsr ___normalizesf
endif_3:
endif_2:
endif_1:
; Join
jsr ___joinsf
return:
; Restore registers
mov.w r2,r6
pop r5
pop r4
rts
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