arch/sparc/lib/mul.S

/* */
   1 /* $Id: mul.S,v 1.2 1995/11/25 00:59:00 davem Exp $
   2  * mul.S:       This routine was taken from glibc-1.09 and is covered
   3  *              by the GNU Library General Public License Version 2.
   4  */
   5 
   6 /*
   7  * Signed multiply, from Appendix E of the Sparc Version 8
   8  * Architecture Manual.
   9  */
  10 
  11 /*
  12  * Returns %o0 * %o1 in %o1%o0 (i.e., %o1 holds the upper 32 bits of
  13  * the 64-bit product).
  14  *
  15  * This code optimizes short (less than 13-bit) multiplies.
  16  */
  17 
  18         .globl .mul
  19 .mul:
  20         mov     %o0, %y         ! multiplier -> Y
  21         andncc  %o0, 0xfff, %g0 ! test bits 12..31
  22         be      Lmul_shortway   ! if zero, can do it the short way
  23         andcc   %g0, %g0, %o4   ! zero the partial product and clear N and V
  24 
  25         /*
  26          * Long multiply.  32 steps, followed by a final shift step.
  27          */
  28         mulscc  %o4, %o1, %o4   ! 1
  29         mulscc  %o4, %o1, %o4   ! 2
  30         mulscc  %o4, %o1, %o4   ! 3
  31         mulscc  %o4, %o1, %o4   ! 4
  32         mulscc  %o4, %o1, %o4   ! 5
  33         mulscc  %o4, %o1, %o4   ! 6
  34         mulscc  %o4, %o1, %o4   ! 7
  35         mulscc  %o4, %o1, %o4   ! 8
  36         mulscc  %o4, %o1, %o4   ! 9
  37         mulscc  %o4, %o1, %o4   ! 10
  38         mulscc  %o4, %o1, %o4   ! 11
  39         mulscc  %o4, %o1, %o4   ! 12
  40         mulscc  %o4, %o1, %o4   ! 13
  41         mulscc  %o4, %o1, %o4   ! 14
  42         mulscc  %o4, %o1, %o4   ! 15
  43         mulscc  %o4, %o1, %o4   ! 16
  44         mulscc  %o4, %o1, %o4   ! 17
  45         mulscc  %o4, %o1, %o4   ! 18
  46         mulscc  %o4, %o1, %o4   ! 19
  47         mulscc  %o4, %o1, %o4   ! 20
  48         mulscc  %o4, %o1, %o4   ! 21
  49         mulscc  %o4, %o1, %o4   ! 22
  50         mulscc  %o4, %o1, %o4   ! 23
  51         mulscc  %o4, %o1, %o4   ! 24
  52         mulscc  %o4, %o1, %o4   ! 25
  53         mulscc  %o4, %o1, %o4   ! 26
  54         mulscc  %o4, %o1, %o4   ! 27
  55         mulscc  %o4, %o1, %o4   ! 28
  56         mulscc  %o4, %o1, %o4   ! 29
  57         mulscc  %o4, %o1, %o4   ! 30
  58         mulscc  %o4, %o1, %o4   ! 31
  59         mulscc  %o4, %o1, %o4   ! 32
  60         mulscc  %o4, %g0, %o4   ! final shift
  61 
  62         ! If %o0 was negative, the result is
  63         !       (%o0 * %o1) + (%o1 << 32))
  64         ! We fix that here.
  65 
  66 #if 0
  67         tst     %o0
  68         bge     1f
  69         rd      %y, %o0
  70 
  71         ! %o0 was indeed negative; fix upper 32 bits of result by subtracting 
  72         ! %o1 (i.e., return %o4 - %o1 in %o1).
  73         retl
  74         sub     %o4, %o1, %o1
  75 
  76 1:
  77         retl
  78         mov     %o4, %o1
  79 #else
  80         /* Faster code adapted from tege@sics.se's code for umul.S.  */
  81         sra     %o0, 31, %o2    ! make mask from sign bit
  82         and     %o1, %o2, %o2   ! %o2 = 0 or %o1, depending on sign of %o0
  83         rd      %y, %o0         ! get lower half of product
  84         retl
  85         sub     %o4, %o2, %o1   ! subtract compensation 
  86                                 !  and put upper half in place
  87 #endif
  88 
  89 Lmul_shortway:
  90         /*
  91          * Short multiply.  12 steps, followed by a final shift step.
  92          * The resulting bits are off by 12 and (32-12) = 20 bit positions,
  93          * but there is no problem with %o0 being negative (unlike above).
  94          */
  95         mulscc  %o4, %o1, %o4   ! 1
  96         mulscc  %o4, %o1, %o4   ! 2
  97         mulscc  %o4, %o1, %o4   ! 3
  98         mulscc  %o4, %o1, %o4   ! 4
  99         mulscc  %o4, %o1, %o4   ! 5
 100         mulscc  %o4, %o1, %o4   ! 6
 101         mulscc  %o4, %o1, %o4   ! 7
 102         mulscc  %o4, %o1, %o4   ! 8
 103         mulscc  %o4, %o1, %o4   ! 9
 104         mulscc  %o4, %o1, %o4   ! 10
 105         mulscc  %o4, %o1, %o4   ! 11
 106         mulscc  %o4, %o1, %o4   ! 12
 107         mulscc  %o4, %g0, %o4   ! final shift
 108 
 109         /*
 110          *  %o4 has 20 of the bits that should be in the low part of the
 111          * result; %y has the bottom 12 (as %y's top 12).  That is:
 112          *
 113          *        %o4               %y
 114          * +----------------+----------------+
 115          * | -12- |   -20-  | -12- |   -20-  |
 116          * +------(---------+------)---------+
 117          *  --hi-- ----low-part----
 118          *
 119          * The upper 12 bits of %o4 should be sign-extended to form the
 120          * high part of the product (i.e., highpart = %o4 >> 20).
 121          */
 122 
 123         rd      %y, %o5
 124         sll     %o4, 12, %o0    ! shift middle bits left 12
 125         srl     %o5, 20, %o5    ! shift low bits right 20, zero fill at left
 126         or      %o5, %o0, %o0   ! construct low part of result
 127         retl
 128         sra     %o4, 20, %o1    ! ... and extract high part of result
/* */
root/arch/sparc/lib/mul.S
