arch/m68k-mac/libgcc1/_divdf3.s

   1 | double floating point divide routine
   2 |
   3 | written by Kai-Uwe Bloem (I5110401@dbstu1.bitnet).
   4 | Based on a 80x86 floating point packet from comp.os.minix, written by P.Housel
   5 |
   6 |
   7 | Revision 1.2, kub 01-90 :
   8 | added support for denormalized numbers
   9 |
  10 | Revision 1.1, kub 12-89 :
  11 | Ported over to 68k assembler
  12 |
  13 | Revision 1.0:
  14 | original 8088 code from P.S.Housel
  15
  16 BIAS8   =       0x3FF-1
  17
  18         .text
  19         .even
  20         .globl  __divdf3
  21         .globl  _infinitydf
  22
  23 __divdf3:
  24         lea     %sp@(4),%a0     | pointer to parameters u and v
  25         moveml  %d2-%d7,%sp@-   | save registers
  26         moveml  %a0@,%d4-%d5/%d6-%d7    | %d4-%d5 = u, %d6-%d7 = v
  27
  28         movel   %d4,%d0         | %d0 = u.exp
  29         swap    %d0
  30         movew   %d0,%d2         | %d2 = u.sign
  31         lsrw    #4,%d0
  32         andw    #0x07ff,%d0     | kill sign bit
  33
  34         movel   %d6,%d1         | %d1 = v.exp
  35         swap    %d1
  36         eorw    %d1,%d2         | %d2 = u.sign ^ v.sign (in bit 31)
  37         lsrw    #4,%d1
  38         andw    #0x07ff,%d1     | kill sign bit
  39
  40         andl    #0x0fffff,%d4   | remove exponent from u.mantissa
  41         tstw    %d0             | check for zero exponent - no leading "1"
  42         beq     L_00
  43         orl     #0x100000,%d4   | restore implied leading "1"
  44         bra     L_10
  45 L_00:   addw    #1,%d0          | "normalize" exponent
  46 L_10:   movel   %d4,%d3
  47         orl     %d5,%d3
  48         beq     retz            | dividing zero
  49
  50         andl    #0x0fffff,%d6   | remove exponent from v.mantissa
  51         tstw    %d1             | check for zero exponent - no leading "1"
  52         beq     L_01
  53         orl     #0x100000,%d6   | restore implied leading "1"
  54         bra     L_11
  55 L_01:   addw    #1,%d1          | "normalize" exponent
  56 L_11:   movel   %d6,%d3
  57         orl     %d7,%d3
  58         beq     divz            | divide by zero
  59
  60         movew   %d2,%a0         | save sign
  61
  62         subw    %d1,%d0         | subtract exponents,
  63         addw    #BIAS8-11+1,%d0 |  add bias back in, account for shift
  64         addw    #66,%d0         |  add loop offset, +2 for extra rounding bits
  65                                 |   for denormalized numbers (2 implied by dbra)
  66         movew   #24,%d1         | bit number for "implied" pos (+4 for rounding)
  67         movel   #-1,%d2         | zero the quotient
  68         movel   #-1,%d3         |  (for speed it is a one's complement)
  69         subl    %d7,%d5         | initial subtraction,
  70         subxl   %d6,%d4         | u = u - v
  71 L_2:
  72         btst    %d1,%d2         | divide until 1 in implied position
  73         beq     L_5
  74
  75         addl    %d5,%d5
  76         addxl   %d4,%d4
  77         bcs     L_4             | if carry is set, add, else subtract
  78
  79         addxl   %d3,%d3         | shift quotient and set bit zero
  80         addxl   %d2,%d2
  81         subl    %d7,%d5         | subtract
  82         subxl   %d6,%d4         | u = u - v
  83         dbra    %d0,L_2         | give up if result is denormalized
  84         bra     L_5
  85 L_4:
  86         addxl   %d3,%d3         | shift quotient and clear bit zero
  87         addxl   %d2,%d2
  88         addl    %d7,%d5         | add (restore)
  89         addxl   %d6,%d4         | u = u + v
  90         dbra    %d0,L_2         | give up if result is denormalized
  91 L_5:    subw    #2,%d0          | remove rounding offset for denormalized nums
  92         notl    %d2             | invert quotient to get it right
  93         notl    %d3
  94
  95         movel   %d2,%d4         | save quotient mantissa
  96         movel   %d3,%d5
  97         movew   %a0,%d2         | get sign back
  98         clrw    %d1             | zero rounding bits
  99         jmp     norm_df         | (registers on stack removed by norm_df)
 100
 101 retz:   clrl    %d0             | zero destination
 102         clrl    %d1
 103         moveml  %sp@+,%d2-%d7
 104         rts                     | no normalization needed
 105
 106 divz:   moveml  _infinitydf,%d0-%d1 | return infinty value
 107         moveml  %sp@+,%d2-%d7   | should really cause trap ?!?
 108         rts