Implement MPI division.

include/cryb/mpi.h

@@ -52,6 +52,8 @@ const char *cryb_mpi_version(void);
 #define mpi_dec			cryb_mpi_dec
 #define mpi_dec_abs		cryb_mpi_dec_abs
 #define mpi_destroy		cryb_mpi_destroy
+#define mpi_div			cryb_mpi_div
+#define mpi_div_abs		cryb_mpi_div_abs
 #define mpi_eq			cryb_mpi_eq
 #define mpi_eq_abs		cryb_mpi_eq_abs
 #define mpi_eq_abs_u32		cryb_mpi_eq_abs_u32
@@ -106,6 +108,8 @@ int mpi_copy(cryb_mpi *, const cryb_mpi *);
 int mpi_dec(cryb_mpi *);
 int mpi_dec_abs(cryb_mpi *);
 void mpi_destroy(cryb_mpi *);
+int mpi_div(cryb_mpi *, cryb_mpi *, const cryb_mpi *, const cryb_mpi *);
+int mpi_div_abs(cryb_mpi *, cryb_mpi *, const cryb_mpi *, const cryb_mpi *);
 int mpi_eq(const cryb_mpi *, const cryb_mpi *);
 int mpi_eq_abs(const cryb_mpi *, const cryb_mpi *);
 int mpi_eq_abs_u32(const cryb_mpi *, uint32_t);

lib/mpi/Makefile.am

@@ -13,6 +13,8 @@ libcryb_mpi_la_SOURCES = \
 	cryb_mpi_dec.c \
 	cryb_mpi_dec_abs.c \
 	cryb_mpi_destroy.c \
+	cryb_mpi_div.c \
+	cryb_mpi_div_abs.c \
 	cryb_mpi_eq.c \
 	cryb_mpi_eq_abs.c \
 	cryb_mpi_eq_i32.c \

lib/mpi/cryb_mpi_div.c

@@ -0,0 +1,54 @@
+/*
+ * Copyright (c) 2017 Dag-Erling Smørgrav
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. The name of the author may not be used to endorse or promote
+ *    products derived from this software without specific prior written
+ *    permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include "cryb/impl.h"
+
+#include <stddef.h>
+#include <stdint.h>
+
+#include <cryb/mpi.h>
+
+#include "cryb_mpi_impl.h"
+
+/*
+ * Store the quotient and remainder of A divided by B in Q and R.
+ */
+int
+mpi_div(cryb_mpi *Q, cryb_mpi *R, const cryb_mpi *A, const cryb_mpi *B)
+{
+	int neg;
+
+	neg = A->neg ^ B->neg;
+	if (mpi_div_abs(Q, R, A, B) < 0)
+		return (-1);
+	if (Q->msb > 0)
+		Q->neg = neg;
+	return (0);
+}
+

lib/mpi/cryb_mpi_div_abs.c

@@ -0,0 +1,115 @@
+/*
+ * Copyright (c) 2017 Dag-Erling Smørgrav
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without
+ * modification, are permitted provided that the following conditions
+ * are met:
+ * 1. Redistributions of source code must retain the above copyright
+ *    notice, this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright
+ *    notice, this list of conditions and the following disclaimer in the
+ *    documentation and/or other materials provided with the distribution.
+ * 3. The name of the author may not be used to endorse or promote
+ *    products derived from this software without specific prior written
+ *    permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR AND CONTRIBUTORS ``AS IS'' AND
+ * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
+ * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
+ * ARE DISCLAIMED.  IN NO EVENT SHALL THE AUTHOR OR CONTRIBUTORS BE LIABLE
+ * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
+ * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
+ * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
+ * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
+ * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
+ * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
+ * SUCH DAMAGE.
+ */
+
+#include "cryb/impl.h"
+
+#include <errno.h>
+#include <stddef.h>
+#include <stdint.h>
+#include <strings.h>
+
+#include <cryb/bitwise.h>
+#include <cryb/mpi.h>
+
+#include "cryb_mpi_impl.h"
+
+/*
+ * Store the quotient and remainder of A divided by B in Q and R.
+ *
+ * Assumes Q != R, but any combination of {Q,R} == {A,B} is fine.  Either
+ * Q or R or both may be NULL, althought the latter is pointless.
+ */
+int
+mpi_div_abs(cryb_mpi *Q, cryb_mpi *R, const cryb_mpi *A, const cryb_mpi *B)
+{
+	cryb_mpi AA = CRYB_MPI_ZERO, QQ = CRYB_MPI_ZERO;
+	int cmp;
+
+	/* trivial cases */
+	if (B->msb == 0) {
+		/* divide something by zero */
+		errno = EINVAL;
+		return (-1);
+	} else if (A->msb == 0) {
+		/* divide zero by something */
+		if (Q != NULL)
+			mpi_zero(Q);
+		if (R != NULL)
+			mpi_zero(R);
+		return (0);
+	} else if (B->msb == 1) {
+		/* divide something by one */
+		if (Q != A && Q != NULL && mpi_copy(Q, A) != 0)
+			return (-1);
+		if (R != NULL)
+			mpi_zero(R);
+		return (0);
+	} else if ((cmp = mpi_cmp_abs(A, B)) == 0) {
+		/* divide something by itself */
+		if (Q != NULL)
+			mpi_set(Q, 1);
+		if (R != NULL)
+			mpi_zero(R);
+		return (0);
+	} else if (cmp < 0) {
+		/* divide something by something larger */
+		if (Q != NULL)
+			mpi_zero(Q);
+		if (R != A && R != NULL && mpi_copy(R, A) != 0)
+			return (-1);
+		return (0);
+	}
+
+	/* division is destructive, so we work on copies */
+	if (mpi_copy(&AA, A) != 0)
+		return (-1);
+	mpi_zero(&QQ);
+
+	/*
+	 * Repeatedly subtract B from A until they are the same length,
+	 * then one last time if A is still greater than B.
+	 */
+	while (AA.msb > B->msb) {
+		mpi_sub_abs(&AA, &AA, B);
+		mpi_inc_abs(&QQ);
+	}
+	if (mpi_cmp_abs(&AA, B) >= 0) {
+		mpi_sub_abs(&AA, &AA, B);
+		mpi_inc_abs(&QQ);
+	}
+
+	/* store result where requested and clean up */
+	if (Q != NULL)
+		mpi_swap(Q, &QQ);
+	if (R != NULL)
+		mpi_swap(R, &AA);
+	mpi_destroy(&AA);
+	mpi_destroy(&QQ);
+	return (0);
+}

t/t_mpi_muldiv.c

@@ -145,42 +145,70 @@ static struct t_div_case {
 	uint8_t b[16];
 	size_t bmsb;
 	int bneg:1;
-	uint8_t e[16];
+	uint8_t q[16];
-	size_t emsb;
+	size_t qmsb;
-	int eneg:1;
+	int qneg:1;
+	uint8_t r[16];
+	size_t rmsb;
+	int rneg:1;
 } t_div_cases[] = {
+	{
+		"0 / 1 == 0",
+		{                                                      },  0, 0,
+		{                                                 0x01 },  1, 0,
+		{                                                      },  0, 0,
+		{                                                      },  0, 0,
+	},
 	{
 		"1 / 1 == 1",
 		{                                                 0x01 },  1, 0,
 		{                                                 0x01 },  1, 0,
 		{                                                 0x01 },  1, 0,
+		{                                                      },  0, 0,
 	},
+	{
+		"4 / 2 == 2",
+		{                                                 0x04 },  3, 0,
+		{                                                 0x02 },  2, 0,
+		{                                                 0x02 },  2, 0,
+		{                                                      },  0, 0,
+	},
+	{
+		"257 / 127 == 2 rem 3",
+		{                                           0x01, 0x01 },  9, 0,
+		{                                                 0x7f },  7, 0,
+		{                                                 0x02 },  2, 0,
+		{                                                 0x03 },  2, 0,
+	},
+	/* XXX needs lots more tests! */
 };
 
 static int
 t_mpi_div_tc(char **desc CRYB_UNUSED, void *arg)
 {
 	struct t_div_case *tc = arg;
-	cryb_mpi a = CRYB_MPI_ZERO, b = CRYB_MPI_ZERO, e = CRYB_MPI_ZERO;
+	cryb_mpi a = CRYB_MPI_ZERO, b = CRYB_MPI_ZERO;
-	cryb_mpi x = CRYB_MPI_ZERO;
+	cryb_mpi q = CRYB_MPI_ZERO, r = CRYB_MPI_ZERO;
+	cryb_mpi eq = CRYB_MPI_ZERO, er = CRYB_MPI_ZERO;
 	int ret = 1;
 
 	mpi_load(&a, tc->a, (tc->amsb + 7) / 8);
 	a.neg = tc->aneg;
 	mpi_load(&b, tc->b, (tc->bmsb + 7) / 8);
 	b.neg = tc->bneg;
-	mpi_load(&e, tc->e, (tc->emsb + 7) / 8);
+	mpi_load(&eq, tc->q, (tc->qmsb + 7) / 8);
-	e.neg = tc->eneg;
+	eq.neg = tc->qneg;
-#if 0
+	mpi_load(&er, tc->r, (tc->rmsb + 7) / 8);
-	ret &= t_compare_i(0, mpi_div_abs(&x, &a, &b));
+	er.neg = tc->rneg;
-#else
+	ret &= t_compare_i(0, mpi_div_abs(&q, &r, &a, &b));
-	mpi_load(&x, tc->e, (tc->emsb + 7) / 8);
+	ret &= t_compare_mpi(&eq, &q);
-#endif
+	ret &= t_compare_mpi(&er, &r);
-	ret &= t_compare_mpi(&e, &x);
 	mpi_destroy(&a);
 	mpi_destroy(&b);
-	mpi_destroy(&e);
+	mpi_destroy(&q);
-	mpi_destroy(&x);
+	mpi_destroy(&r);
+	mpi_destroy(&eq);
+	mpi_destroy(&er);
 	return (ret);
 }