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Digital Research
This commit is contained in:
Sepp J Morris
2020-11-06 18:50:37 +01:00
parent 621ed8ccaf
commit 31738079c4
8481 changed files with 1888323 additions and 0 deletions
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51
CPM OPERATING SYSTEMS/CPM 68K/1.0X SOURCES/v101/c/libf/ffptnorm.s Normal file
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ttl ffp transcendental normalize internal routine (ffptnorm)
ffptnorm idnt 1,2 ffp transcendental internal normalize
xdef ffptnorm
section 9
***************************************
* (c) copyright 1981 by motorola inc. *
***************************************
******************************
* ffptnorm *
* normalize bin(29,31) value *
* and convert to float *
* *
* input: d6 - internal fixed *
* output: d6 - ffp float *
* cc - reflect value *
* notes: *
* 1) d4 is destroyed. *
* *
* time: (8mhz no wait state) *
* zero 4.0 microsec. *
* avg else 17.0 microsec. *
* *
******************************
ffptnorm move.l #$42,d4 setup initial exponent
tst.l d6 test for non-negative
beq.s fsfrtn return if zero
bpl.s fsfpls branch is >= 0
neg.l d6 absolutize input
move.b #$c2,d4 setup initial negative exponent
fsfpls cmp.l #$00007fff,d6 test for a small number
bhi.s fsfcont branch if not small
swap.w d6 swap halves
sub.b #16,d4 offset by 16 shifts
fsfcont add.l d6,d6 shift another bit
dbmi d4,fsfcont shift left until normalized
tst.b d6 ? should we round up
bpl.s fsfnrm no, branch rounded
add.l #$100,d6 round up
bcc.s fsfnrm branch no overflow
roxr.l #1,d6 adjust back for bit in 31
add.b #1,d4 make up for last shift right
fsfnrm move.b d4,d6 insert sign+exponent
fsfrtn rts return to caller
end