Inline BN_reciprocal() in its only caller

This is simpler, doesn't need an auxiliary function of dubious value,
avouds an auxiliary variable and gets rid of a bunch of comments that
are hard to make sense of.

This doesn't bother to invalidate recp->shift since on error you should
not be reusing the RECP_CTX without reinitializing it.

ok jsing

1 files changed, 10 insertions, 36 deletions

diff --git a/src/lib/libcrypto/bn/bn_recp.c b/src/lib/libcrypto/bn/bn_recp.c
index 757ed0c3d2..d5070bc003 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 1.31 2025/02/04 05:09:53 tb Exp $ */
+/* $OpenBSD: bn_recp.c,v 1.32 2025/02/04 12:47:58 tb Exp $ */
 /* Copyright (C) 1995-1998 Eric Young (eay@cryptsoft.com)
  * All rights reserved.
  *
@@ -104,34 +104,6 @@ BN_RECP_CTX_free(BN_RECP_CTX *recp)
         freezero(recp, sizeof(*recp));
 }
 
-/* len is the expected size of the result
- * We actually calculate with an extra word of precision, so
- * we can do faster division if the remainder is not required.
- */
-/* r := 2^len / m */
-static int
-BN_reciprocal(BIGNUM *r, const BIGNUM *m, int len, BN_CTX *ctx)
-{
-        int ret = -1;
-        BIGNUM *t;
-
-        BN_CTX_start(ctx);
-        if ((t = BN_CTX_get(ctx)) == NULL)
-                goto err;
-
-        if (!BN_set_bit(t, len))
-                goto err;
-
-        if (!BN_div_ct(r, NULL, t, m, ctx))
-                goto err;
-
-        ret = len;
-
-err:
-        BN_CTX_end(ctx);
-        return ret;
-}
-
 int
 BN_div_reciprocal(BIGNUM *dv, BIGNUM *rem, const BIGNUM *m, BN_RECP_CTX *recp,
     BN_CTX *ctx)
@@ -174,13 +146,15 @@ BN_div_reciprocal(BIGNUM *dv, BIGNUM *rem, const BIGNUM *m, BN_RECP_CTX *recp,
         if (j > i)
                 i = j;
 
-        /* Nr := round(2^i / N) */
-        if (i != recp->shift)
-                recp->shift = BN_reciprocal(recp->Nr, recp->N, i, ctx);
-
-        /* BN_reciprocal returns i, or -1 for an error */
-        if (recp->shift == -1)
-                goto err;
+        /* Compute Nr := (1 << i) / N if necessary. */
+        if (i != recp->shift) {
+                BN_zero(recp->Nr);
+                if (!BN_set_bit(recp->Nr, i))
+                        goto err;
+                if (!BN_div_ct(recp->Nr, NULL, recp->Nr, recp->N, ctx))
+                        goto err;
+                recp->shift = i;
+        }
 
         /* d := |round(round(m / 2^BN_num_bits(N)) * recp->Nr / 2^(i - BN_num_bits(N)))|
          *    = |round(round(m / 2^BN_num_bits(N)) * round(2^i / N) / 2^(i - BN_num_bits(N)))|