arch/m68k-mac/libgcc1/_extend.s

   1 | single float to double float conversion 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 BIAS4   =       0x7F-1
  17 BIAS8   =       0x3FF-1
  18
  19         .text
  20         .even
  21         .globl  __extendsfdf2
  22
  23 __extendsfdf2:
  24         lea     %sp@(4),%a0     | parameter pointer
  25         moveml  %d2-%d7,%sp@-   | save regs to keep norm_df happy
  26         movel   %a0@,%d4                | get number
  27         clrl    %d5             | prepare double mantissa
  28
  29         movew   %a0@,%d0                | extract exponent
  30         movew   %d0,%d2         | extract sign
  31         lsrw    #7,%d0
  32         andw    #0xff,%d0       | kill sign bit (exponent is 8 bits)
  33
  34         andl    #0x7fffff,%d4   | remove exponent from mantissa
  35         tstw    %d0             | check for zero exponent - no leading "1"
  36         beq     L_0             | for denormalized numbers
  37         orl     #0x800000,%d4   | restore implied leading "1"
  38         bra     L_1
  39 L_0:    addw    #1,%d0          | "normalize" exponent
  40 L_1:
  41         addw    #BIAS8-BIAS4-3,%d0      | adjust bias, account for shift
  42         clrw    %d1             | dummy rounding info
  43
  44         jmp     norm_df