From a11c52e896dad5c8123b3246648fc669a9f8a205 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Dag-Erling=20Sm=C3=B8rgrav?= <des@des.no>
Date: Wed, 29 Mar 2017 19:56:53 +0200
Subject: [PATCH] Refactor the comparison predicates, check for identity first.

---
 lib/mpi/cryb_mpi_cmp.c     | 17 ++++++-----------
 lib/mpi/cryb_mpi_cmp_abs.c |  4 +++-
 lib/mpi/cryb_mpi_eq.c      |  7 +++++--
 lib/mpi/cryb_mpi_eq_abs.c  |  7 +++++--
 t/t_mpi_compar.c           | 29 +++++++++++++++++++++++++++++
 5 files changed, 48 insertions(+), 16 deletions(-)

diff --git a/lib/mpi/cryb_mpi_cmp.c b/lib/mpi/cryb_mpi_cmp.c
index 9fef809..690e546 100644
--- a/lib/mpi/cryb_mpi_cmp.c
+++ b/lib/mpi/cryb_mpi_cmp.c
@@ -43,15 +43,10 @@ int
 mpi_cmp(const cryb_mpi *X, const cryb_mpi *Y)
 {
 
-	if (X->neg) {
-		if (Y->neg)
-			return (-mpi_cmp_abs(X, Y));
-		else
-			return (-1);
-	} else {
-		if (Y->neg)
-			return (1);
-		else
-			return (mpi_cmp_abs(X, Y));
-	}
+	if (X == Y)
+		return (0);
+	else if (X->neg)
+		return (Y->neg ? -mpi_cmp_abs(X, Y) : -1);
+	else
+		return (Y->neg ? 1 : mpi_cmp_abs(X, Y));
 }
diff --git a/lib/mpi/cryb_mpi_cmp_abs.c b/lib/mpi/cryb_mpi_cmp_abs.c
index bbe8a30..4484534 100644
--- a/lib/mpi/cryb_mpi_cmp_abs.c
+++ b/lib/mpi/cryb_mpi_cmp_abs.c
@@ -44,7 +44,9 @@ mpi_cmp_abs(const cryb_mpi *X, const cryb_mpi *Y)
 {
 	int i;
 
-	/* check width first  */
+	/* check trivial cases first  */
+	if (X == Y)
+		return (0);
 	if (X->msb > Y->msb)
 		return (1);
 	if (X->msb < Y->msb)
diff --git a/lib/mpi/cryb_mpi_eq.c b/lib/mpi/cryb_mpi_eq.c
index 90410d3..2ea3a54 100644
--- a/lib/mpi/cryb_mpi_eq.c
+++ b/lib/mpi/cryb_mpi_eq.c
@@ -43,6 +43,9 @@ int
 mpi_eq(const cryb_mpi *A, const cryb_mpi *B)
 {
 
-	return (A->neg == B->neg && A->msb == B->msb &&
-	    memcmp(A->words, B->words, (A->msb + 31) / 32) == 0);
+	if (A == B)
+		return (1);
+	if (A->neg != B->neg || A->msb != B->msb)
+		return (0);
+	return (memcmp(A->words, B->words, (A->msb + 31) / 32) == 0);
 }
diff --git a/lib/mpi/cryb_mpi_eq_abs.c b/lib/mpi/cryb_mpi_eq_abs.c
index 5e65715..7e0e21d 100644
--- a/lib/mpi/cryb_mpi_eq_abs.c
+++ b/lib/mpi/cryb_mpi_eq_abs.c
@@ -43,6 +43,9 @@ int
 mpi_eq_abs(const cryb_mpi *A, const cryb_mpi *B)
 {
 
-	return (A->msb == B->msb &&
-	    memcmp(A->words, B->words, (A->msb + 31) / 32) == 0);
+	if (A == B)
+		return (1);
+	if (A->msb != B->msb)
+		return (0);
+	return (memcmp(A->words, B->words, (A->msb + 31) / 32) == 0);
 }
diff --git a/t/t_mpi_compar.c b/t/t_mpi_compar.c
index 5e43363..03f30c2 100644
--- a/t/t_mpi_compar.c
+++ b/t/t_mpi_compar.c
@@ -142,6 +142,33 @@ t_mpi_eq(char **desc CRYB_UNUSED, void *arg)
 	return (ret);
 }
 
+/*
+ * Compare an MPI with itself
+ */
+static int
+t_mpi_cmp_ident(char **desc CRYB_UNUSED, void *arg CRYB_UNUSED)
+{
+	cryb_mpi a = CRYB_MPI_ZERO;
+	int ret = 1;
+
+	mpi_set(&a, CRYB_TO);
+	ret &= t_compare_i(0, mpi_cmp(&a, &a));
+	mpi_destroy(&a);
+	return (ret);
+}
+
+static int
+t_mpi_eq_ident(char **desc CRYB_UNUSED, void *arg CRYB_UNUSED)
+{
+	cryb_mpi a = CRYB_MPI_ZERO;
+	int ret = 1;
+
+	mpi_set(&a, CRYB_TO);
+	ret &= t_compare_i(1, mpi_eq(&a, &a));
+	mpi_destroy(&a);
+	return (ret);
+}
+
 /*
  * Compare an MPI with an integer
  */
@@ -187,9 +214,11 @@ t_prepare(int argc, char *argv[])
 	t_mpi_prepare();
 
 	/* comparison */
+	t_add_test(t_mpi_cmp_ident, NULL, "mpi cmp mpi (identity)");
 	for (i = 0; i < sizeof t_cmp_cases / sizeof t_cmp_cases[0]; ++i)
 		t_add_test(t_mpi_cmp, &t_cmp_cases[i],
 		    "mpi cmp mpi (%s)", t_cmp_cases[i].desc);
+	t_add_test(t_mpi_eq_ident, NULL, "mpi eq mpi (identity)");
 	for (i = 0; i < sizeof t_cmp_cases / sizeof t_cmp_cases[0]; ++i)
 		t_add_test(t_mpi_eq, &t_cmp_cases[i],
 		    "mpi eq mpi (%s)", t_cmp_cases[i].desc);