sysdeps/m88k/mul_1.s

   1 ; mc88100 __mpn_mul_1 -- Multiply a limb vector with a single limb and
   2 ; store the product in a second limb vector.
   3
   4 ; Copyright (C) 1992, 1994, 1995 Free Software Foundation, Inc.
   5
   6 ; This file is part of the GNU MP Library.
   7
   8 ; The GNU MP Library is free software; you can redistribute it and/or modify
   9 ; it under the terms of the GNU Library General Public License as published by
  10 ; the Free Software Foundation; either version 2 of the License, or (at your
  11 ; option) any later version.
  12
  13 ; The GNU MP Library is distributed in the hope that it will be useful, but
  14 ; WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY
  15 ; or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU Library General Public
  16 ; License for more details.
  17
  18 ; You should have received a copy of the GNU Library General Public License
  19 ; along with the GNU MP Library; see the file COPYING.LIB.  If not, write to
  20 ; the Free Software Foundation, Inc., 59 Temple Place - Suite 330, Boston,
  21 ; MA 02111-1307, USA.
  22
  23
  24 ; INPUT PARAMETERS
  25 ; res_ptr       r2
  26 ; s1_ptr        r3
  27 ; size          r4
  28 ; s2_limb       r5
  29
  30 ; Common overhead is about 11 cycles/invocation.
  31
  32 ; The speed for S2_LIMB >= 0x10000 is approximately 21 cycles/limb.  (The
  33 ; pipeline stalls 2 cycles due to WB contention.)
  34
  35 ; The speed for S2_LIMB < 0x10000 is approximately 16 cycles/limb.  (The
  36 ; pipeline stalls 2 cycles due to WB contention and 1 cycle due to latency.)
  37
  38 ; To enhance speed:
  39 ; 1. Unroll main loop 4-8 times.
  40 ; 2. Schedule code to avoid WB contention.  It might be tempting to move the
  41 ;    ld instruction in the loops down to save 2 cycles (less WB contention),
  42 ;    but that looses because the ultimate value will be read from outside
  43 ;    the allocated space.  But if we handle the ultimate multiplication in
  44 ;    the tail, we can do this.
  45 ; 3. Make the multiplication with less instructions.  I think the code for
  46 ;    (S2_LIMB >= 0x10000) is not minimal.
  47 ; With these techniques the (S2_LIMB >= 0x10000) case would run in 17 or
  48 ; less cycles/limb; the (S2_LIMB < 0x10000) case would run in 11
  49 ; cycles/limb.  (Assuming infinite unrolling.)
  50
  51         text
  52         align    16
  53         global   ___mpn_mul_1
  54 ___mpn_mul_1:
  55
  56         ; Make S1_PTR and RES_PTR point at the end of their blocks
  57         ; and negate SIZE.
  58         lda      r3,r3[r4]
  59         lda      r6,r2[r4]      ; RES_PTR in r6 since r2 is retval
  60         subu     r4,r0,r4
  61
  62         addu.co  r2,r0,r0       ; r2 = cy = 0
  63         ld       r9,r3[r4]
  64         mask     r7,r5,0xffff   ; r7 = lo(S2_LIMB)
  65         extu     r8,r5,16       ; r8 = hi(S2_LIMB)
  66         bcnd.n   eq0,r8,Lsmall  ; jump if (hi(S2_LIMB) == 0)
  67          subu    r6,r6,4
  68
  69 ; General code for any value of S2_LIMB.
  70
  71         ; Make a stack frame and save r25 and r26
  72         subu     r31,r31,16
  73         st.d     r25,r31,8
  74
  75         ; Enter the loop in the middle
  76         br.n    L1
  77         addu     r4,r4,1
  78
  79 Loop:   ld       r9,r3[r4]
  80         st       r26,r6[r4]
  81 ; bcnd  ne0,r0,0                ; bubble
  82         addu     r4,r4,1
  83 L1:     mul      r26,r9,r5      ; low word of product   mul_1   WB ld
  84         mask     r12,r9,0xffff  ; r12 = lo(s1_limb)     mask_1
  85         mul      r11,r12,r7     ; r11 =  prod_0         mul_2   WB mask_1
  86         mul      r10,r12,r8     ; r10 = prod_1a         mul_3
  87         extu     r13,r9,16      ; r13 = hi(s1_limb)     extu_1  WB mul_1
  88         mul      r12,r13,r7     ; r12 = prod_1b         mul_4   WB extu_1
  89         mul      r25,r13,r8     ; r25  = prod_2         mul_5   WB mul_2
  90         extu     r11,r11,16     ; r11 = hi(prod_0)      extu_2  WB mul_3
  91         addu     r10,r10,r11    ;                       addu_1  WB extu_2
  92 ; bcnd  ne0,r0,0                ; bubble                        WB addu_1
  93         addu.co  r10,r10,r12    ;                               WB mul_4
  94         mask.u   r10,r10,0xffff ; move the 16 most significant bits...
  95         addu.ci  r10,r10,r0     ; ...to the low half of the word...
  96         rot      r10,r10,16     ; ...and put carry in pos 16.
  97         addu.co  r26,r26,r2     ; add old carry limb
  98         bcnd.n   ne0,r4,Loop
  99          addu.ci r2,r25,r10     ; compute new carry limb
 100
 101         st       r26,r6[r4]
 102         ld.d     r25,r31,8
 103         jmp.n    r1
 104          addu    r31,r31,16
 105
 106 ; Fast code for S2_LIMB < 0x10000
 107 Lsmall:
 108         ; Enter the loop in the middle
 109         br.n    SL1
 110         addu     r4,r4,1
 111
 112 SLoop:  ld       r9,r3[r4]      ;
 113         st       r8,r6[r4]      ;
 114         addu     r4,r4,1        ;
 115 SL1:    mul      r8,r9,r5       ; low word of product
 116         mask     r12,r9,0xffff  ; r12 = lo(s1_limb)
 117         extu     r13,r9,16      ; r13 = hi(s1_limb)
 118         mul      r11,r12,r7     ; r11 =  prod_0
 119         mul      r12,r13,r7     ; r12 = prod_1b
 120         addu.cio r8,r8,r2       ; add old carry limb
 121         extu     r10,r11,16     ; r11 = hi(prod_0)
 122         addu     r10,r10,r12    ;
 123         bcnd.n   ne0,r4,SLoop
 124         extu     r2,r10,16      ; r2 = new carry limb
 125
 126         jmp.n    r1
 127         st       r8,r6[r4]