utils: Added chunk_to_dec() function

src/libstrongswan/utils/chunk.c

@@ -1,5 +1,6 @@
 /*
  * Copyright (C) 2008-2019 Tobias Brunner
+ * Copyright (C) 2023 Andreas Steffen
  * Copyright (C) 2005-2006 Martin Willi
  * Copyright (C) 2005 Jan Hutter
  *
@@ -744,6 +745,71 @@ chunk_t chunk_to_base32(chunk_t chunk, char *buf)
 	return chunk_create(buf, len * 8 / 5);
 }
 
+/**
+ * Described in header.
+ */
+chunk_t chunk_to_dec(chunk_t chunk, char *buf)
+{
+	int len, i, i_buf, i_bin = 0;
+	uint16_t remainder;
+	chunk_t bin;
+
+	/* Determine the number of needed decimal digits:
+	 * 10^len > 2^(8*chunk.len)       =>
+	 *    len > log(256) * chunk.len  =>
+	 *    len >   2.4083 * chunk.len
+	 */
+	len = (int)(2.4083 * (double)chunk.len) + 1;
+
+	if (!buf)
+	{
+		buf = malloc(len + 1);
+	}
+	i_buf = len;
+	buf[i_buf] = '\0';
+	bin = chunk_clone(chunk);
+	while (i_bin < bin.len)
+	{
+		remainder = 0;
+		for (i = i_bin; i < bin.len; i++)
+		{
+			remainder = bin.ptr[i] + (remainder << 8);
+			if (remainder < 10)
+			{
+				remainder = bin.ptr[i];
+				bin.ptr[i] = 0;
+				if (i == i_bin)
+				{
+					i_bin++;
+				}
+			}
+			else
+			{
+				bin.ptr[i] = remainder / 10;
+				remainder %= 10;
+			}
+		}
+		if (i_buf > 0)
+		{
+			buf[--i_buf] = 0x30 + remainder;
+		}
+	}
+	chunk_free(&bin);
+
+	/* align decimal number to the start of the string */
+	if (i_buf > 0)
+	{
+		len -= i_buf;
+
+		for (i = 0; i <= len; i++)
+		{
+			buf[i] = buf[i + i_buf];
+		}
+	}
+
+	return chunk_create(buf, len);
+}
+
 /**
  * Described in header.
  */

src/libstrongswan/utils/chunk.h

@@ -1,5 +1,6 @@
 /*
  * Copyright (C) 2008-2019 Tobias Brunner
+ * Copyright (C) 2023 Andreas Steffen
  * Copyright (C) 2005-2008 Martin Willi
  * Copyright (C) 2005 Jan Hutter
  *
@@ -213,6 +214,18 @@ chunk_t chunk_from_base64(chunk_t base64, char *buf);
  */
 chunk_t chunk_to_base32(chunk_t chunk, char *buf);
 
+/**
+ * Convert a chunk of data to decimal encoding.
+ *
+ * The resulting string is '\\0' terminated, but the chunk does not include
+ * the '\\0'. If buf is supplied, it must hold at least (chunk.len * 2.41 + 1).
+ *
+ * @param chunk         data to convert to decimal encoding
+ * @param buf           buffer to write to, NULL to malloc
+ * @return              chunk of encoded data
+ */
+chunk_t chunk_to_dec(chunk_t chunk, char *buf);
+
 /**
  * Free contents of a chunk
  */