reactos/lib/rtl/i386/aullrem_asm.s

   1 /*
   2  * COPYRIGHT:         See COPYING in the top level directory
   3  * PROJECT:           ReactOS kernel
   4  * PURPOSE:           Run-Time Library
   5  * FILE:              lib/rtl/i386/aullrem.S
   6  * PROGRAMER:         Alex Ionescu (alex@relsoft.net)
   7  *                    Eric Kohl (ekohl@rz-online.de)
   8  *
   9  * Copyright (C) 2002 Michael Ringgaard.
  10  * All rights reserved.
  11  *
  12  * Redistribution and use in source and binary forms, with or without
  13  * modification, are permitted provided that the following conditions
  14  * are met:
  15  *
  16  * 1. Redistributions of source code must retain the above copyright
  17  *    notice, this list of conditions and the following disclaimer.
  18  * 2. Redistributions in binary form must reproduce the above copyright
  19  *    notice, this list of conditions and the following disclaimer in the
  20  *    documentation and/or other materials provided with the distribution.
  21  * 3. Neither the name of the project nor the names of its contributors
  22  *    may be used to endorse or promote products derived from this software
  23  *    without specific prior written permission.
  24
  25  * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS "AS IS" AND
  26  * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
  27  * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
  28  * ARE DISCLAIMED.  IN NO EVENT SHALL THE COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE
  29  * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
  30  * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
  31  * OR SERVICES// LOSS OF USE, DATA, OR PROFITS// OR BUSINESS INTERRUPTION)
  32  * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
  33  * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
  34  * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
  35  * SUCH DAMAGE.
  36  */
  37
  38 .globl __aullrem
  39
  40  /* DATA ********************************************************************/
  41
  42 fzero:
  43         .long   0                       // Floating point zero
  44         .long   0                       // Floating point zero
  45
  46 __fltused:
  47         .long 0x9875
  48
  49 .intel_syntax noprefix
  50
  51 /* FUNCTIONS ***************************************************************/
  52
  53 //
  54 // ullrem - unsigned long remainder
  55 //
  56 // Purpose:
  57 //       Does a unsigned long remainder of the arguments.  Arguments are
  58 //       not changed.
  59 //
  60 // Entry:
  61 //       Arguments are passed on the stack:
  62 //               1st pushed: divisor (QWORD)
  63 //               2nd pushed: dividend (QWORD)
  64 //
  65 // Exit:
  66 //       EDX:EAX contains the remainder (dividend%divisor)
  67 //       NOTE: this routine removes the parameters from the stack.
  68 //
  69 // Uses:
  70 //       ECX
  71 //
  72
  73 __aullrem:
  74
  75         push    ebx
  76
  77 // Set up the local stack and save the index registers.  When this is done
  78 // the stack frame will look as follows (assuming that the expression a%b will
  79 // generate a call to ullrem(a, b)):
  80 //
  81 //               -----------------
  82 //               |               |
  83 //               |---------------|
  84 //               |               |
  85 //               |--divisor (b)--|
  86 //               |               |
  87 //               |---------------|
  88 //               |               |
  89 //               |--dividend (a)-|
  90 //               |               |
  91 //               |---------------|
  92 //               | return addr** |
  93 //               |---------------|
  94 //       ESP---->|      EBX      |
  95 //               -----------------
  96 //
  97
  98 #undef DVNDLO
  99 #undef DVNDHI
 100 #undef DVSRLO
 101 #undef DVSRHI
 102 #define DVNDLO  [esp + 8]       // stack address of dividend (a)
 103 #define DVNDHI  [esp + 8]       // stack address of dividend (a)
 104 #define DVSRLO  [esp + 16]      // stack address of divisor (b)
 105 #define DVSRHI  [esp + 20]      // stack address of divisor (b)
 106
 107 // Now do the divide.  First look to see if the divisor is less than 4194304K.
 108 // If so, then we can use a simple algorithm with word divides, otherwise
 109 // things get a little more complex.
 110 //
 111
 112         mov     eax,DVSRHI // check to see if divisor < 4194304K
 113         or      eax,eax
 114         jnz     short ...L1        // nope, gotta do this the hard way
 115         mov     ecx,DVSRLO // load divisor
 116         mov     eax,DVNDHI // load high word of dividend
 117         xor     edx,edx
 118         div     ecx             // edx <- remainder, eax <- quotient
 119         mov     eax,DVNDLO // edx:eax <- remainder:lo word of dividend
 120         div     ecx             // edx <- final remainder
 121         mov     eax,edx         // edx:eax <- remainder
 122         xor     edx,edx
 123         jmp     short ...L2        // restore stack and return
 124
 125 //
 126 // Here we do it the hard way.  Remember, eax contains DVSRHI
 127 //
 128
 129 ...L1:
 130         mov     ecx,eax         // ecx:ebx <- divisor
 131         mov     ebx,DVSRLO
 132         mov     edx,DVNDHI // edx:eax <- dividend
 133         mov     eax,DVNDLO
 134 ...L3:
 135         shr     ecx,1           // shift divisor right one bit// hi bit <- 0
 136         rcr     ebx,1
 137         shr     edx,1           // shift dividend right one bit// hi bit <- 0
 138         rcr     eax,1
 139         or      ecx,ecx
 140         jnz     short ...L3        // loop until divisor < 4194304K
 141         div     ebx             // now divide, ignore remainder
 142
 143 //
 144 // We may be off by one, so to check, we will multiply the quotient
 145 // by the divisor and check the result against the orignal dividend
 146 // Note that we must also check for overflow, which can occur if the
 147 // dividend is close to 2**64 and the quotient is off by 1.
 148 //
 149
 150         mov     ecx,eax         // save a copy of quotient in ECX
 151         mul     dword ptr DVSRHI
 152         xchg    ecx,eax         // put partial product in ECX, get quotient in EAX
 153         mul     dword ptr DVSRLO
 154         add     edx,ecx         // EDX:EAX = QUOT * DVSR
 155         jc      short ...L4        // carry means Quotient is off by 1
 156
 157 //
 158 // do long compare here between original dividend and the result of the
 159 // multiply in edx:eax.  If original is larger or equal, we're ok, otherwise
 160 // subtract the original divisor from the result.
 161 //
 162
 163         cmp     edx,DVNDHI // compare hi words of result and original
 164         ja      short ...L4        // if result > original, do subtract
 165         jb      short ...L5        // if result < original, we're ok
 166         cmp     eax,DVNDLO // hi words are equal, compare lo words
 167         jbe     short ...L5        // if less or equal we're ok, else subtract
 168 ...L4:
 169         sub     eax,DVSRLO // subtract divisor from result
 170         sbb     edx,DVSRHI
 171 ...L5:
 172
 173 //
 174 // Calculate remainder by subtracting the result from the original dividend.
 175 // Since the result is already in a register, we will perform the subtract in
 176 // the opposite direction and negate the result to make it positive.
 177 //
 178
 179         sub     eax,DVNDLO // subtract original dividend from result
 180         sbb     edx,DVNDHI
 181         neg     edx             // and negate it
 182         neg     eax
 183         sbb     edx,0
 184
 185 //
 186 // Just the cleanup left to do.  dx:ax contains the remainder.
 187 // Restore the saved registers and return.
 188 //
 189
 190 ...L2:
 191
 192         pop     ebx
 193
 194         ret     16