arch/m68k-all/libgcc1/_addsubdf3.s

   1 | double floating point add/subtract 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 1.3, kub 01-90 :
   8 | added support for denormalized numbers
   9 |
  10 | Revision 1.2, kub 01-90 :
  11 | replace far shifts by swaps to gain speed
  12 |
  13 | Revision 1.1, kub 12-89 :
  14 | Ported over to 68k assembler
  15 |
  16 | Revision 1.0:
  17 | original 8088 code from P.S.Housel
  18
  19         .text
  20         .even
  21         .globl  __subdf3
  22         .globl  __adddf3
  23
  24 __subdf3:
  25         eorb    #0x80,%sp@(12)  | reverse sign of v
  26 __adddf3:
  27         lea     %sp@(4),%a0     | pointer to u and v parameter
  28         moveml  %d2-%d7,%sp@-   | save registers
  29         moveml  %a0@,%d4-%d5/%d6-%d7    | %d4-%d5 = v, %d6-%d7 = u
  30
  31         movel   %d6,%d0         | %d0 = u.exp
  32         swap    %d0
  33         movel   %d6,%d2         | %d2.h = u.sign
  34         movew   %d0,%d2
  35         lsrw    #4,%d0
  36         andw    #0x07ff,%d0     | kill sign bit
  37
  38         movel   %d4,%d1         | %d1 = v.exp
  39         swap    %d1
  40         eorw    %d1,%d2         | %d2.l = u.sign ^ v.sign
  41         lsrw    #4,%d1
  42         andw    #0x07ff,%d1     | kill sign bit
  43
  44         andl    #0x0fffff,%d6   | remove exponent from u.mantissa
  45         tstw    %d0             | check for zero exponent - no leading "1"
  46         beq     L_00
  47         orl     #0x100000,%d6   | restore implied leading "1"
  48         bra     L_10
  49 L_00:   addw    #1,%d0          | "normalize" exponent
  50 L_10:
  51         andl    #0x0fffff,%d4   | remove exponent from v.mantissa
  52         tstw    %d1             | check for zero exponent - no leading "1"
  53         beq     L_01
  54         orl     #0x100000,%d4   | restore implied leading "1"
  55         bra     L_11
  56 L_01:   addw    #1,%d1          | "normalize" exponent
  57 L_11:
  58         clrw    %d3             | (put initial zero rounding bits in %d3)
  59         negw    %d1             | %d1 = u.exp - v.exp
  60         addw    %d0,%d1
  61         beq     L_5             | exponents are equal - no shifting neccessary
  62         bgt     L_12            | not equal but no exchange neccessary
  63         exg     %d4,%d6         | exchange u and v
  64         exg     %d5,%d7
  65         subw    %d1,%d0         | %d0 = u.exp - (u.exp - v.exp) = v.exp
  66         negw    %d1
  67         tstw    %d2             | %d2.h = u.sign ^ (u.sign ^ v.sign) = v.sign
  68         bpl     L_12
  69         bchg    #31,%d2
  70 L_12:
  71         cmpw    #53,%d1         | is u so much bigger that v is not
  72         bge     L_7             | significant ?
  73
  74         movew   #10-1,%d3       | shift u left up to 10 bits to minimize loss
  75 L_2:
  76         addl    %d7,%d7
  77         addxl   %d6,%d6
  78         subw    #1,%d0          | decrement exponent
  79         subw    #1,%d1          | done shifting altogether ?
  80         dbeq    %d3,L_2         | loop if still can shift u.mant more
  81         clrw    %d3
  82 L_3:
  83         cmpw    #16,%d1         | see if fast rotate possible
  84         blt     L_4
  85         orb     %d5,%d3         | set rounding bits
  86         orb     %d2,%d3
  87         sne     %d2             | "sticky byte"
  88         movew   %d5,%d3
  89         lsrw    #8,%d3
  90         movew   %d4,%d5         | rotate by swapping register halfs
  91         swap    %d5
  92         clrw    %d4
  93         swap    %d4
  94         subw    #16,%d1
  95         bra     L_3
  96 L_0:
  97         lsrl    #1,%d4          | shift v.mant right the rest of the way
  98         roxrl   #1,%d5          | to line it up with u.mant
  99         orb     %d3,%d2         | set "sticky byte" if necessary
 100         roxrw   #1,%d3          | shift into rounding bits
 101 L_4:    dbra    %d1,L_0         | loop
 102         andb    #1,%d2          | see if "sticky bit" should be set
 103         orb     %d2,%d3
 104 L_5:
 105         tstw    %d2             | are the signs equal ?
 106         bpl     L_6             | yes, no negate necessary
 107
 108         negb    %d3             | negate rounding bits and v.mant
 109         negl    %d5
 110         negxl   %d4
 111 L_6:
 112         addl    %d5,%d7         | u.mant = u.mant + v.mant
 113         addxl   %d4,%d6
 114         bcs     L_7             | needn't negate
 115         tstw    %d2             | opposite signs ?
 116         bpl     L_7             | don't need to negate result
 117
 118         negb    %d3             | negate rounding bits and u.mant
 119         negl    %d7
 120         negxl   %d6
 121         notl    %d2             | switch sign
 122 L_7:
 123         movel   %d6,%d4         | move result for normalization
 124         movel   %d7,%d5
 125         moveb   %d3,%d1         | put rounding bits in %d1 for norm_df
 126         swap    %d2             | put sign into %d2 (exponent is in %d0)
 127         jmp     norm_df         | leave registers on stack for norm_df