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Fix msb calculation. We may have to backtrack quite a bit, for

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instance when subtracting two nearly equal large numbers.
This commit is contained in:
Dag-Erling Smørgrav 2014-12-30 16:45:18 +00:00 committed by des
parent 2027ce33e7
commit 0d483f20ab
1 changed files with 3 additions and 3 deletions
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6
lib/mpi/mpi_sub.c
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@ -64,7 +64,7 @@ mpi_sub_abs(cryb_mpi *X, cryb_mpi *A, cryb_mpi *B)
L = B, G = A; L = B, G = A;
/* make sure X is large enough for the largest possible result */ /* make sure X is large enough for the largest possible result */
if (mpi_grow(X, G->msb)) if (mpi_grow(X, G->msb) != 0)
return (-1); return (-1);
/* subtract B from A word by word until we run out of B */ /* subtract B from A word by word until we run out of B */
@ -77,9 +77,9 @@ mpi_sub_abs(cryb_mpi *X, cryb_mpi *A, cryb_mpi *B)
while (c) { while (c) {
X->words[i] = G->words[i] - c; X->words[i] = G->words[i] - c;
c = (G->words[i] > c); c = (G->words[i] > c);
i += c; ++i;
} }
if (X->words[i] == 0) while (i > 0 && X->words[i] == 0)
--i; --i;
/* compute msb of msw */ /* compute msb of msw */
/* XXX use flsl() */ /* XXX use flsl() */