linux-kernel - [PATCH 10/14] crypto: ecc - Implement ecc_digits_to

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Date: Thu,  8 Feb 2024 17:18:36 -0500
From: Stefan Berger <stefanb@...ux.ibm.com>
To: keyrings@...r.kernel.org, linux-crypto@...r.kernel.org,
        herbert@...dor.apana.org.au, davem@...emloft.net
Cc: linux-kernel@...r.kernel.org, saulo.alessandre@....jus.br,
        Stefan Berger <stefanb@...ux.ibm.com>
Subject: [PATCH 10/14] crypto: ecc - Implement ecc_digits_to_array to convert digits to byte array

Implement ecc_digits_to_array to convert an array of ndigits into an
nbytes-sized byte array.

Signed-off-by: Stefan Berger <stefanb@...ux.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 22931f0c7295..75ee113f58f9 100644
--- a/include/crypto/internal/ecc.h
+++ b/include/crypto/internal/ecc.h
@@ -75,6 +75,24 @@ static inline void ecc_digits_from_array(const u8 *in, unsigned int nbytes,
 	ecc_swap_digits(tmp, out, ndigits);
 }
 
+/**
+ * ecc_digits_to_array() - Copy nbytes from an ndigits array into a byte array
+ * @in:      Input digits array
+ * @ndigits: Number of digits in input digits array
+ * @out:     Output byte array
+ * @nbytes:  Number of digits to create from byte array
+ */
+static inline void ecc_digits_to_array(const u64 *in, unsigned int ndigits,
+				       u8 *out, unsigned int nbytes)
+{
+	unsigned int sz = ndigits * sizeof(u64);
+	u8 tmp[ECC_MAX_DIGITS * sizeof(u64)];
+	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