93 lines
2 KiB
C
93 lines
2 KiB
C
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/*++
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Copyright (c) 1989 Microsoft Corporation
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Module Name:
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recip.c
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Abstract:
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This module generates reciprocol fractions for implementing integer
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division by multiplication.
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Author:
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David N. Cutler (davec) 13-May-1989
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Environment:
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User mode.
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Revision History:
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--*/
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#include <stdio.h>
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typedef struct _large_integer {
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unsigned long LowPart;
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long HighPart;
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} large_integer;
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//long Divisors[] = {2, 4, 8, 16, 32, 64, 128, 256, 512, 1024, 2048, 4096, 8192, 0};
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long Divisors[] = {10, 10000, 10000000, 86400000, 0};
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void
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main (argc, argv)
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int argc;
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char *argv[];
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{
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large_integer Fraction;
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long Index;
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long NumberBits;
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long Remainder;
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long i;
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//
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// Compute first few reciprocols.
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//
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for (Index = Divisors[i = 0]; Index != 0L; Index = Divisors[++i]) {
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NumberBits = 0L;
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Remainder = 1L;
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Fraction.LowPart = 0L;
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Fraction.HighPart = 0L;
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while (Fraction.HighPart >= 0L) {
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NumberBits += 1L;
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Fraction.HighPart <<= 1L;
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if ((Fraction.LowPart & 0x80000000) != 0L) {
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Fraction.HighPart += 1L;
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}
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Fraction.LowPart <<= 1L;
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Remainder <<= 1L;
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if (Remainder >= Index) {
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Remainder -= Index;
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Fraction.LowPart |= 1L;
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}
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}
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if (Remainder) {
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if ((Fraction.LowPart == -1L) && (Fraction.HighPart == -1L)) {
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Fraction.LowPart = 0L;
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Fraction.HighPart = 0x80000000;
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NumberBits -= 1L;
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} else {
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if (Fraction.LowPart == -1L) {
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Fraction.LowPart = 0L;
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Fraction.HighPart += 1L;
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} else {
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Fraction.LowPart += 1L;
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}
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}
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}
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printf("Divisor %2ld, Fraction %8lx, %8lx Shift %ld\n", Index,
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Fraction.HighPart, Fraction.LowPart, NumberBits - 64L);
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}
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return;
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}
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