2 * COPYRIGHT: See COPYING in the top level directory
3 * PROJECT: ReactOS kernel
4 * PURPOSE: Run-Time Library
5 * FILE: lib/sdk/crt/math/i386/aullrem_asm.s
6 * PROGRAMER: Alex Ionescu (alex@relsoft.net)
8 * Copyright (C) 2002 Michael Ringgaard.
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12 * modification, are permitted provided that the following conditions
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41 /* FUNCTIONS ***************************************************************/
45 // ullrem - unsigned long remainder
48 // Does a unsigned long remainder of the arguments. Arguments are
52 // Arguments are passed on the stack:
53 // 1st pushed: divisor (QWORD)
54 // 2nd pushed: dividend (QWORD)
57 // EDX:EAX contains the remainder (dividend%divisor)
58 // NOTE: this routine removes the parameters from the stack.
68 // Set up the local stack and save the index registers. When this is done
69 // the stack frame will look as follows (assuming that the expression a%b will
70 // generate a call to ullrem(a, b)):
93 #define DVNDLO [esp + 8] // stack address of dividend (a)
94 #define DVNDHI [esp + 12] // stack address of dividend (a)
95 #define DVSRLO [esp + 16] // stack address of divisor (b)
96 #define DVSRHI [esp + 20] // stack address of divisor (b)
98 // Now do the divide. First look to see if the divisor is less than 4194304K.
99 // If so, then we can use a simple algorithm with word divides, otherwise
100 // things get a little more complex.
103 mov eax,DVSRHI // check to see if divisor < 4194304K
105 jnz short .L1 // nope, gotta do this the hard way
106 mov ecx,DVSRLO // load divisor
107 mov eax,DVNDHI // load high word of dividend
109 div ecx // edx <- remainder, eax <- quotient
110 mov eax,DVNDLO // edx:eax <- remainder:lo word of dividend
111 div ecx // edx <- final remainder
112 mov eax,edx // edx:eax <- remainder
114 jmp short .L2 // restore stack and return
117 // Here we do it the hard way. Remember, eax contains DVSRHI
121 mov ecx,eax // ecx:ebx <- divisor
123 mov edx,DVNDHI // edx:eax <- dividend
126 shr ecx,1 // shift divisor right one bit// hi bit <- 0
128 shr edx,1 // shift dividend right one bit// hi bit <- 0
131 jnz short .L3 // loop until divisor < 4194304K
132 div ebx // now divide, ignore remainder
135 // We may be off by one, so to check, we will multiply the quotient
136 // by the divisor and check the result against the orignal dividend
137 // Note that we must also check for overflow, which can occur if the
138 // dividend is close to 2**64 and the quotient is off by 1.
141 mov ecx,eax // save a copy of quotient in ECX
143 xchg ecx,eax // put partial product in ECX, get quotient in EAX
145 add edx,ecx // EDX:EAX = QUOT * DVSR
146 jc short .L4 // carry means Quotient is off by 1
149 // do long compare here between original dividend and the result of the
150 // multiply in edx:eax. If original is larger or equal, we're ok, otherwise
151 // subtract the original divisor from the result.
154 cmp edx,DVNDHI // compare hi words of result and original
155 ja short .L4 // if result > original, do subtract
156 jb short .L5 // if result < original, we're ok
157 cmp eax,DVNDLO // hi words are equal, compare lo words
158 jbe short .L5 // if less or equal we're ok, else subtract
160 sub eax,DVSRLO // subtract divisor from result
165 // Calculate remainder by subtracting the result from the original dividend.
166 // Since the result is already in a register, we will perform the subtract in
167 // the opposite direction and negate the result to make it positive.
170 sub eax,DVNDLO // subtract original dividend from result
172 neg edx // and negate it
177 // Just the cleanup left to do. dx:ax contains the remainder.
178 // Restore the saved registers and return.