[PATCH v2 10/14] crypto: ecc - Implement ecc_digits_to_bytes to convert digits to byte array

From: Stefan Berger <stefanb@linux.ibm.com>
To: keyrings@vger.kernel.org, linux-crypto@vger.kernel.org,
	herbert@gondor.apana.org.au, davem@davemloft.net
Cc: linux-kernel@vger.kernel.org, saulo.alessandre@tse.jus.br,
	Stefan Berger <stefanb@linux.ibm.com>
Subject: [PATCH v2 10/14] crypto: ecc - Implement ecc_digits_to_bytes to convert digits to byte array
Date: Thu, 15 Feb 2024 18:14:09 -0500	[thread overview]
Message-ID: <20240215231414.3857320-11-stefanb@linux.ibm.com> (raw)
In-Reply-To: <20240215231414.3857320-1-stefanb@linux.ibm.com>

Implement ecc_digits_to_bytes to convert an array of digits into an
nbytes-sized byte array.

Signed-off-by: Stefan Berger <stefanb@linux.ibm.com>
---
 include/crypto/internal/ecc.h | 18 ++++++++++++++++++
 1 file changed, 18 insertions(+)

diff --git a/include/crypto/internal/ecc.h b/include/crypto/internal/ecc.h
index b8ca5023b3b5..6229aa3f3218 100644
--- a/include/crypto/internal/ecc.h
+++ b/include/crypto/internal/ecc.h
@@ -75,6 +75,24 @@ static inline void ecc_digits_from_bytes(const u8 *in, unsigned int nbytes,
 	ecc_swap_digits(tmp, out, ndigits);
 }
 
+/**
+ * ecc_digits_to_bytes() - Copy digits into a byte array of size nbytes
+ * @in:      Input digits array
+ * @ndigits: Number of digits in input digits array
+ * @out:     Output byte array
+ * @nbytes:  Number of bytes to copy into byte array
+ */
+static inline void ecc_digits_to_bytes(const u64 *in, unsigned int ndigits,
+				       u8 *out, unsigned int nbytes)
+{
+	unsigned int sz = ndigits << ECC_DIGITS_TO_BYTES_SHIFT;
+	u8 tmp[ECC_MAX_DIGITS << ECC_DIGITS_TO_BYTES_SHIFT];
+	unsigned int o = sz - nbytes;
+
+	ecc_swap_digits(in, (u64 *)tmp, ndigits);
+	memcpy(out, &tmp[o], nbytes);
+}
+
 /**
  * ecc_is_key_valid() - Validate a given ECDH private key
  *
-- 
2.43.0

