Add chex

Author: pennam

src/hex/README.md

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+# chex
+
+[chex.h](chex.h) file implement hex encoding/decoding basic functions by Tero 'stedo' Liukko under a MIT license.  https://github.com/stedonet/chex

src/hex/chex.h

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+/*
+MIT License
+
+Copyright (c) 2022 Tero 'stedo' Liukko. https://github.com/stedonet/chex
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.
+*/
+
+#ifndef STEDO_CHEX_H
+#define STEDO_CHEX_H
+
+/**
+ * @brief check whether given ASCII character is a hexadecimal digit
+ * @param[in] h ASCII character to decode
+ * @return TRUE if h is hexadecimal, FALSE otherwise
+**/
+#pragma GCC diagnostic push
+#pragma GCC diagnostic ignored "-Wunused-function"
+static unsigned chex_isxdigit(unsigned h){
+  unsigned char n09 = h - '0';
+  unsigned char nAF = (h | 0x20) - 'a';
+  return (n09 <= (9 - 0)) || (nAF <= (0xf - 0xa));
+}
+#pragma GCC diagnostic pop
+
+/**
+ * @brief encode nibble to hexadecimal ASCII character
+ * @param[in] nibble value to encode
+ * @return hexadecimal ASCII value
+ * @note the four most significant bits are ignored
+**/
+static char chex_toxdigit(unsigned nibble){
+  const char* lut = "0123456789abcdef";
+  return lut[nibble & 0xf];
+}
+
+
+/**
+ * @brief decode a single case-insensitive hexadecimal ASCII character to its decimal value
+ * @param[in] h ASCII character to decode
+ * @return decimal value of the input
+ * @note the input is assumed to be a valid
+**/
+static unsigned char chex_fromxdigit(unsigned h){
+  return ((h & 0xf) + (h >> 6) * 9);
+}
+
+
+/**
+ * @brief encode an array of bytes to an array of hexadecimal ASCII characters
+ * @param[out]  hex   buffer to write to
+ * @param[in]   hlen  maximum number of characters to write
+ * @param[in]   bin   array of bytes to encode
+ * @param[in]   blen  number of bytes to encode
+ * @return number of characters written
+ * @note null terminator is not included in the output
+**/
+static unsigned chex_encode(char* hex, unsigned hlen, const void* bin, unsigned blen){
+  const unsigned char* b = (const unsigned char*)bin;
+  unsigned i, j;
+  for(i = 0, j = 0; (i < blen) && (j+1 < hlen); ++i, j+=2){
+    hex[j+0] = chex_toxdigit(b[i]>>4);
+    hex[j+1] = chex_toxdigit(b[i]>>0);
+  }
+  return j;
+}
+
+
+/**
+ * @brief decode an array of hexadecimal ASCII characters to an array of bytes
+ * @param[out]  bin   buffer to write to
+ * @param[in]   blen  maximum number of bytes to write
+ * @param[in]   hex   array of hex characters to decode
+ * @param[in]   hlen  number of hex characters to decode
+ * @return number of bytes written
+ * @note hex input is assumed valid and its length a multiple of two
+**/
+static unsigned chex_decode(void* bin, unsigned blen, const char* hex, unsigned hlen){
+  unsigned i, j;
+  for(i = 0, j = 0; (i < blen) && (j+1 < hlen); ++i, j+=2){
+    unsigned char hi = chex_fromxdigit(hex[j+0]);
+    unsigned char lo = chex_fromxdigit(hex[j+1]);
+    ((unsigned char*)bin)[i] = (hi << 4) | lo;
+  }
+  return i;
+}
+
+#endif /* STEDO_CHEX_H */