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_truncdf.cpp
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1992-12-12
|
2KB
|
100 lines
| not needed with -__M68881__
#ifndef __M68881__
.text
.even
.globl __truncdfsf2, ___truncdfsf2
__truncdfsf2:
___truncdfsf2:
# ifdef sfp004
| double float to single float conversion routine
| oflow checking is omitted. The ''881 returns a signed infinity.
|
| Written by M.Ritzert
| 5.10.90
| ritzert@dfg.dbp.de
|
| addresses of the 68881 data port. This choice is fastest when much data is
| transferred between the two processors.
comm = -6
resp = -16
zahl = 0
| waiting loop ...
|
| wait:
| ww: cmpiw #0x8900,a1@(resp)
| beq ww
| is coded directly by
| .long 0x0c688900, 0xfff067f8
lea 0xfffffa50:w,a0
movew #0x5400,a0@(comm) | load double to fp0
cmpiw #0x8900,a0@(resp) | check
movel a7@(4),a0@ | push arguments
movel a7@(8),a0@ |
movew #0x6400,a0@(comm) | result (real) to d0
.long 0x0c688900, 0xfff067f8
movel a0@,d0
rts
# else sfp004
| double float to single float conversion routine
|
| written by Kai-Uwe Bloem (I5110401@dbstu1.bitnet).
| Based on a 80x86 floating point packet from comp.os.minix, written by P.Housel
|
|
| Revision 1.2, kub 01-90 :
| added support for denormalized numbers
|
| Revision 1.1, kub 12-89 :
| Ported over to 68k assembler
|
| Revision 1.0:
| original 8088 code from P.S.Housel
BIAS4 = 0x7F-1
BIAS8 = 0x3FF-1
lea sp@(4),a0 | parameter pointer
moveml d2-d5,sp@- | save regs
moveml a0@,d4-d5 | get number
movew a0@,d0 | extract exponent
movew d0,d2 | extract sign
lsrw #4,d0
andw #0x7ff,d0 | kill sign bit
andl #0x0fffff,d4 | remove exponent from mantissa
tstw d0 | check for zero exponent - no leading "1"
beq 0f | for denormalized numbers
orl #0x100000,d4 | restore implied leading "1"
bra 1f
0: addw #1,d0 | "normalize" exponent
1:
addw #BIAS4-BIAS8,d0 | adjust bias
addl d5,d5 | shift up to realign mantissa for floats
addxl d4,d4
addl d5,d5
addxl d4,d4
addl d5,d5
addxl d4,d4
movel d5,d1 | set rounding bits
roll #8,d1
andl #0x00ffffff,d5 | check to see if sticky bit should be set
beq 2f
orb #1,d1 | set sticky bit
2:
jmp norm_sf | (leave regs on stack for norm_sf)
# endif sfp004
#endif __M68881__