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https://github.com/cryb-to/cryb-to.git
synced 2024-11-22 05:35:46 +00:00
In both mpi_add_abs() and mpi_sub_abs(), make sure that the target is
untouched if the operation fails. Also ensure that A = A +/- A works.
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commit
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2 changed files with 54 additions and 25 deletions
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@ -36,7 +36,6 @@
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/*
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* Store the sum of the absolutes values of A and B in X.
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* XXX safe for either A or B to be the same object as X but not both
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*/
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int
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mpi_add_abs(cryb_mpi *X, cryb_mpi *A, cryb_mpi *B)
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@ -44,36 +43,53 @@ mpi_add_abs(cryb_mpi *X, cryb_mpi *A, cryb_mpi *B)
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unsigned int i;
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uint32_t c;
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if (X == B)
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B = A, A = X;
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if (X != A)
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mpi_copy(X, A);
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/* 0 + 0 = 0 */
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if (X->msb == 0 && B->msb == 0)
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/*
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* Trivial cases: A and B are identical and / or both zero.
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*/
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if (A->msb == 0 && B->msb == 0)
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return (0);
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/* make room */
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if (mpi_grow(X, X->msb + 1) != 0 || mpi_grow(X, B->msb + 1) != 0)
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if (A == B) {
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if (X != A && mpi_copy(X, A) != 0)
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return (-1);
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return (mpi_lshift(X, 1));
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}
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/*
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* Normalize our operands: if X is identical to either A or B, we
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* want it to be A. Otherwise, copy A into X. In either case,
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* make sure X is large enough for the largest possible sum.
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*/
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if (X == B) {
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B = A;
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A = X;
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}
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if (mpi_grow(X, A->msb + 1) != 0 || mpi_grow(X, B->msb + 1) != 0)
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return (-1);
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if (X != A)
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/* this cannot fail */
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mpi_copy(X, A);
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/*
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* From now on, we are adding B to X and A is irrelevant.
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*/
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/* add B into X word by word until we run out of B */
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for (c = i = 0; i < (B->msb + 31) / 32; ++i) {
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// fprintf(stderr, "0x%08x + 0x%08x (%u)", X->words[i], B->words[i], c);
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X->words[i] += c;
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c = (X->words[i] < c);
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X->words[i] += B->words[i];
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c += (X->words[i] < B->words[i]);
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// fprintf(stderr, " = 0x%08x (%u)\n", X->words[i], c);
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}
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/* keep propagating carry */
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while (c) {
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// fprintf(stderr, "0x%08x + 0x%08x (%u)", X->words[i], 0, c);
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X->words[i] += c;
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c = (X->words[i] < c);
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// fprintf(stderr, " = 0x%08x (%u)\n", X->words[i], c);
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++i;
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}
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if (X->words[i] == 0)
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--i;
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/* compute msb of msw */
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/* XXX should use flsl() */
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for (X->msb = 31; X->msb > 0; --X->msb)
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if (X->words[i] & (1 << X->msb))
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break;
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@ -36,7 +36,6 @@
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/*
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* Store the difference between the absolute values of A and B in X.
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* XXX safe for either A or B to be the same object as X but not both
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*/
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int
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mpi_sub_abs(cryb_mpi *X, cryb_mpi *A, cryb_mpi *B)
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@ -44,36 +43,50 @@ mpi_sub_abs(cryb_mpi *X, cryb_mpi *A, cryb_mpi *B)
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unsigned int i;
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uint32_t c;
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if (X == B)
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B = A, A = X;
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if (X != A)
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mpi_copy(X, A);
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/* 0 - 0 = 0 */
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if (X->msb == 0 && B->msb == 0)
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/*
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* Trivial cases: A and B are identical and / or both zero.
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*/
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if (A == B || (A->msb == 0 && B->msb == 0)) {
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mpi_zero(X);
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return (0);
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/* make room */
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}
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/*
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* Normalize our operands: if X is identical to either A or B, we
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* want it to be A. Otherwise, copy A into X. In either case,
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* make sure X is large enough for the largest possible sum.
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*/
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if (X == B && A != B) {
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B = A;
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A = X;
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}
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if (mpi_grow(X, X->msb) != 0 || mpi_grow(X, B->msb) != 0)
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return (-1);
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if (X != A)
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/* this cannot fail */
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mpi_copy(X, A);
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/*
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* From now on, we are subtracting B from X and A is irrelevant.
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*/
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/* subtract B from X word by word until we run out of B */
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for (c = i = 0; i < (B->msb + 31) / 32; ++i) {
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// fprintf(stderr, "0x%08x + 0x%08x (%u)", X->words[i], B->words[i], c);
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X->words[i] -= c;
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c = (X->words[i] > c);
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X->words[i] -= B->words[i];
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c += (X->words[i] > B->words[i]);
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// fprintf(stderr, " = 0x%08x (%u)\n", X->words[i], c);
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}
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/* keep propagating carry */
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while (c) {
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// fprintf(stderr, "0x%08x + 0x%08x (%u)", X->words[i], 0, c);
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X->words[i] -= c;
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c = (X->words[i] > c);
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// fprintf(stderr, " = 0x%08x (%u)\n", X->words[i], c);
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++i;
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}
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if (X->words[i] == 0)
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--i;
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/* compute msb of msw */
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/* XXX use flsl() */
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for (X->msb = 31; X->msb > 0; --X->msb)
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if (X->words[i] & (1 << X->msb))
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break;
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