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107 lines
2.5 KiB
C
107 lines
2.5 KiB
C
/* DIGIT.C - digit arithmetic routines
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*/
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/* Copyright (C) RSA Laboratories, a division of RSA Data Security,
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Inc., created 1991. All rights reserved.
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*/
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#include "global.h"
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#include "rsaref.h"
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#include "nn.h"
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#include "digit.h"
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/* Computes a = b * c, where b and c are digits.
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Lengths: a[2].
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*/
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void NN_DigitMult (a, b, c)
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NN_DIGIT a[2], b, c;
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{
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NN_DIGIT t, u;
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NN_HALF_DIGIT bHigh, bLow, cHigh, cLow;
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bHigh = (NN_HALF_DIGIT)HIGH_HALF (b);
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bLow = (NN_HALF_DIGIT)LOW_HALF (b);
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cHigh = (NN_HALF_DIGIT)HIGH_HALF (c);
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cLow = (NN_HALF_DIGIT)LOW_HALF (c);
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a[0] = (NN_DIGIT)bLow * (NN_DIGIT)cLow;
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t = (NN_DIGIT)bLow * (NN_DIGIT)cHigh;
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u = (NN_DIGIT)bHigh * (NN_DIGIT)cLow;
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a[1] = (NN_DIGIT)bHigh * (NN_DIGIT)cHigh;
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if ((t += u) < u)
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a[1] += TO_HIGH_HALF (1);
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u = TO_HIGH_HALF (t);
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if ((a[0] += u) < u)
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a[1]++;
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a[1] += HIGH_HALF (t);
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}
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/* Sets a = b / c, where a and c are digits.
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Lengths: b[2].
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Assumes b[1] < c and HIGH_HALF (c) > 0. For efficiency, c should be
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normalized.
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*/
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void NN_DigitDiv (a, b, c)
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NN_DIGIT *a, b[2], c;
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{
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NN_DIGIT t[2], u, v;
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NN_HALF_DIGIT aHigh, aLow, cHigh, cLow;
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cHigh = (NN_HALF_DIGIT)HIGH_HALF (c);
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cLow = (NN_HALF_DIGIT)LOW_HALF (c);
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t[0] = b[0];
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t[1] = b[1];
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/* Underestimate high half of quotient and subtract.
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*/
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if (cHigh == MAX_NN_HALF_DIGIT)
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aHigh = (NN_HALF_DIGIT)HIGH_HALF (t[1]);
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else
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aHigh = (NN_HALF_DIGIT)(t[1] / (cHigh + 1));
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u = (NN_DIGIT)aHigh * (NN_DIGIT)cLow;
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v = (NN_DIGIT)aHigh * (NN_DIGIT)cHigh;
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if ((t[0] -= TO_HIGH_HALF (u)) > (MAX_NN_DIGIT - TO_HIGH_HALF (u)))
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t[1]--;
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t[1] -= HIGH_HALF (u);
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t[1] -= v;
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/* Correct estimate.
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*/
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while ((t[1] > cHigh) ||
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((t[1] == cHigh) && (t[0] >= TO_HIGH_HALF (cLow)))) {
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if ((t[0] -= TO_HIGH_HALF (cLow)) > MAX_NN_DIGIT - TO_HIGH_HALF (cLow))
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t[1]--;
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t[1] -= cHigh;
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aHigh++;
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}
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/* Underestimate low half of quotient and subtract.
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*/
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if (cHigh == MAX_NN_HALF_DIGIT)
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aLow = (NN_HALF_DIGIT)LOW_HALF (t[1]);
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else
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aLow =
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(NN_HALF_DIGIT)((TO_HIGH_HALF (t[1]) + HIGH_HALF (t[0])) / (cHigh + 1));
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u = (NN_DIGIT)aLow * (NN_DIGIT)cLow;
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v = (NN_DIGIT)aLow * (NN_DIGIT)cHigh;
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if ((t[0] -= u) > (MAX_NN_DIGIT - u))
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t[1]--;
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if ((t[0] -= TO_HIGH_HALF (v)) > (MAX_NN_DIGIT - TO_HIGH_HALF (v)))
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t[1]--;
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t[1] -= HIGH_HALF (v);
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/* Correct estimate.
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*/
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while ((t[1] > 0) || ((t[1] == 0) && t[0] >= c)) {
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if ((t[0] -= c) > (MAX_NN_DIGIT - c))
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t[1]--;
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aLow++;
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}
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*a = TO_HIGH_HALF (aHigh) + aLow;
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}
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