From a8409a544cf836e1e561b3794aeafbe161f747ed Mon Sep 17 00:00:00 2001
From: tb <>
Date: Tue, 4 Feb 2025 05:09:53 +0000
Subject: Start cleaning up BN_div_reciprocal() a bit

The fast path where no division is performed can be dealt with without
BN_CTX, so do that up front so there's no need to clean up before return.
Error check BN_CTX_get() on each use asd simplify the logic for optional
input parameters. KNF for an ugly comment.

ok jsing
---
 src/lib/libcrypto/bn/bn_recp.c | 47 +++++++++++++++++++++---------------------
 1 file changed, 23 insertions(+), 24 deletions(-)

diff --git a/src/lib/libcrypto/bn/bn_recp.c b/src/lib/libcrypto/bn/bn_recp.c
index 8f917e95db..757ed0c3d2 100644
--- a/src/lib/libcrypto/bn/bn_recp.c
+++ b/src/lib/libcrypto/bn/bn_recp.c
@@ -1,4 +1,4 @@
-/* $OpenBSD: bn_recp.c,v 1.30 2025/01/22 12:53:16 tb Exp $ */
+/* $OpenBSD: bn_recp.c,v 1.31 2025/02/04 05:09:53 tb Exp $ */
 /* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)
  * All rights reserved.
  *
@@ -139,34 +139,33 @@ BN_div_reciprocal(BIGNUM *dv, BIGNUM *rem, const BIGNUM *m, BN_RECP_CTX *recp,
 	int i, j, ret = 0;
 	BIGNUM *a, *b, *d, *r;
 
+	if (BN_ucmp(m, recp->N) < 0) {
+		if (dv != NULL)
+			BN_zero(dv);
+		if (rem != NULL)
+			return bn_copy(rem, m);
+		return 1;
+	}
+
 	BN_CTX_start(ctx);
-	a = BN_CTX_get(ctx);
-	b = BN_CTX_get(ctx);
-	if (dv != NULL)
-		d = dv;
-	else
+	if ((a = BN_CTX_get(ctx)) == NULL)
+		goto err;
+	if ((b = BN_CTX_get(ctx)) == NULL)
+		goto err;
+
+	if ((d = dv) == NULL)
 		d = BN_CTX_get(ctx);
-	if (rem != NULL)
-		r = rem;
-	else
-		r = BN_CTX_get(ctx);
-	if (a == NULL || b == NULL || d == NULL || r == NULL)
+	if (d == NULL)
 		goto err;
 
-	if (BN_ucmp(m, recp->N) < 0) {
-		BN_zero(d);
-		if (!bn_copy(r, m)) {
-			BN_CTX_end(ctx);
-			return 0;
-		}
-		BN_CTX_end(ctx);
-		return 1;
-	}
+	if ((r = rem) == NULL)
+		r = BN_CTX_get(ctx);
+	if (r == NULL)
+		goto err;
 
-	/* We want the remainder
-	 * Given input of ABCDEF / ab
-	 * we need multiply ABCDEF by 3 digests of the reciprocal of ab
-	 *
+	/*
+	 * We want the remainder. Given input of ABCDEF / ab we need to
+	 * multiply ABCDEF by 3 digits of the reciprocal of ab.
 	 */
 
 	/* i := max(BN_num_bits(m), 2*BN_num_bits(N)) */
-- 
cgit v1.2.3-55-g6feb