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In both mpi_add_abs() and mpi_sub_abs(), make sure that the target is

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untouched if the operation fails.  Also ensure that A = A +/- A works.
This commit is contained in:
Dag-Erling Smørgrav 2014-12-29 23:44:34 +00:00 committed by des
parent 98c6349d4a
commit bc8e9d67ba
2 changed files with 54 additions and 25 deletions
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42
lib/mpi/mpi_add.c
View file

@ -36,7 +36,6 @@
/* /*
* Store the sum of the absolutes values of A and B in X. * Store the sum of the absolutes values of A and B in X.
* XXX safe for either A or B to be the same object as X but not both
*/ */
int int
mpi_add_abs(cryb_mpi *X, cryb_mpi *A, cryb_mpi *B) mpi_add_abs(cryb_mpi *X, cryb_mpi *A, cryb_mpi *B)
@ -44,36 +43,53 @@ mpi_add_abs(cryb_mpi *X, cryb_mpi *A, cryb_mpi *B)
unsigned int i; unsigned int i;
uint32_t c; uint32_t c;
if (X == B) /*
B = A, A = X; * Trivial cases: A and B are identical and / or both zero.
if (X != A) */
mpi_copy(X, A); if (A->msb == 0 && B->msb == 0)
/* 0 + 0 = 0 */
if (X->msb == 0 && B->msb == 0)
return (0); return (0);
/* make room */ if (A == B) {
if (mpi_grow(X, X->msb + 1) != 0 || mpi_grow(X, B->msb + 1) != 0) if (X != A && mpi_copy(X, A) != 0)
return (-1);
return (mpi_lshift(X, 1));
}
/*
* Normalize our operands: if X is identical to either A or B, we
* want it to be A. Otherwise, copy A into X. In either case,
* make sure X is large enough for the largest possible sum.
*/
if (X == B) {
B = A;
A = X;
}
if (mpi_grow(X, A->msb + 1) != 0 || mpi_grow(X, B->msb + 1) != 0)
return (-1); return (-1);
if (X != A)
/* this cannot fail */
mpi_copy(X, A);
/*
* From now on, we are adding B to X and A is irrelevant.
*/
/* add B into X word by word until we run out of B */ /* add B into X word by word until we run out of B */
for (c = i = 0; i < (B->msb + 31) / 32; ++i) { for (c = i = 0; i < (B->msb + 31) / 32; ++i) {
// fprintf(stderr, "0x%08x + 0x%08x (%u)", X->words[i], B->words[i], c);
X->words[i] += c; X->words[i] += c;
c = (X->words[i] < c); c = (X->words[i] < c);
X->words[i] += B->words[i]; X->words[i] += B->words[i];
c += (X->words[i] < B->words[i]); c += (X->words[i] < B->words[i]);
// fprintf(stderr, " = 0x%08x (%u)\n", X->words[i], c);
} }
/* keep propagating carry */ /* keep propagating carry */
while (c) { while (c) {
// fprintf(stderr, "0x%08x + 0x%08x (%u)", X->words[i], 0, c);
X->words[i] += c; X->words[i] += c;
c = (X->words[i] < c); c = (X->words[i] < c);
// fprintf(stderr, " = 0x%08x (%u)\n", X->words[i], c);
++i; ++i;
} }
if (X->words[i] == 0) if (X->words[i] == 0)
--i; --i;
/* compute msb of msw */ /* compute msb of msw */
/* XXX should use flsl() */
for (X->msb = 31; X->msb > 0; --X->msb) for (X->msb = 31; X->msb > 0; --X->msb)
if (X->words[i] & (1 << X->msb)) if (X->words[i] & (1 << X->msb))
break; break;

37
lib/mpi/mpi_sub.c
View file

@ -36,7 +36,6 @@
/* /*
* Store the difference between the absolute values of A and B in X. * Store the difference between the absolute values of A and B in X.
* XXX safe for either A or B to be the same object as X but not both
*/ */
int int
mpi_sub_abs(cryb_mpi *X, cryb_mpi *A, cryb_mpi *B) mpi_sub_abs(cryb_mpi *X, cryb_mpi *A, cryb_mpi *B)
@ -44,36 +43,50 @@ mpi_sub_abs(cryb_mpi *X, cryb_mpi *A, cryb_mpi *B)
unsigned int i; unsigned int i;
uint32_t c; uint32_t c;
if (X == B) /*
B = A, A = X; * Trivial cases: A and B are identical and / or both zero.
if (X != A) */
mpi_copy(X, A); if (A == B || (A->msb == 0 && B->msb == 0)) {
/* 0 - 0 = 0 */ mpi_zero(X);
if (X->msb == 0 && B->msb == 0)
return (0); return (0);
/* make room */ }
/*
* Normalize our operands: if X is identical to either A or B, we
* want it to be A. Otherwise, copy A into X. In either case,
* make sure X is large enough for the largest possible sum.
*/
if (X == B && A != B) {
B = A;
A = X;
}
if (mpi_grow(X, X->msb) != 0 || mpi_grow(X, B->msb) != 0) if (mpi_grow(X, X->msb) != 0 || mpi_grow(X, B->msb) != 0)
return (-1); return (-1);
if (X != A)
/* this cannot fail */
mpi_copy(X, A);
/*
* From now on, we are subtracting B from X and A is irrelevant.
*/
/* subtract B from X word by word until we run out of B */ /* subtract B from X word by word until we run out of B */
for (c = i = 0; i < (B->msb + 31) / 32; ++i) { for (c = i = 0; i < (B->msb + 31) / 32; ++i) {
// fprintf(stderr, "0x%08x + 0x%08x (%u)", X->words[i], B->words[i], c);
X->words[i] -= c; X->words[i] -= c;
c = (X->words[i] > c); c = (X->words[i] > c);
X->words[i] -= B->words[i]; X->words[i] -= B->words[i];
c += (X->words[i] > B->words[i]); c += (X->words[i] > B->words[i]);
// fprintf(stderr, " = 0x%08x (%u)\n", X->words[i], c);
} }
/* keep propagating carry */ /* keep propagating carry */
while (c) { while (c) {
// fprintf(stderr, "0x%08x + 0x%08x (%u)", X->words[i], 0, c);
X->words[i] -= c; X->words[i] -= c;
c = (X->words[i] > c); c = (X->words[i] > c);
// fprintf(stderr, " = 0x%08x (%u)\n", X->words[i], c);
++i; ++i;
} }
if (X->words[i] == 0) if (X->words[i] == 0)
--i; --i;
/* compute msb of msw */ /* compute msb of msw */
/* XXX use flsl() */
for (X->msb = 31; X->msb > 0; --X->msb) for (X->msb = 31; X->msb > 0; --X->msb)
if (X->words[i] & (1 << X->msb)) if (X->words[i] & (1 << X->msb))
break; break;