From 86d2648ccad546ddf5f0fea7847ef66fa41a8d8e Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Nils=20O=2E=20Sel=C3=A5sdal?= <nos@utel.tech>
Date: Tue, 11 Aug 2026 23:36:48 +0200
Subject: [PATCH] Add hex encoding/decoding

---
 src/main.c   | 28 ++++++++++++++++++++++++++++
 src/string.c | 52 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 src/string.h | 34 +++++++++++++++++++++++++++++++++-
 3 files changed, 113 insertions(+), 1 deletion(-)

diff --git a/src/main.c b/src/main.c
index df8a0fe..3294857 100644
--- a/src/main.c
+++ b/src/main.c
@@ -533,6 +533,33 @@ void string_test_utf8(void)
     TRACEF("str4:\n");
     print_runes(str4);  // this should be a valid code point
 
+}
+
+void string_test_hex(void)
+{
+    MArena arena;
+    U8 data[4096];
+    marena_init(&arena, data, sizeof data);
+    Allocator allocator = marena_allocator(&arena);
+
+    Str str1 = S("Hello World ☺");
+
+    Str str1_encoded = str_hex_encode_alloc(&allocator, str1);
+    printf("str1_encoded: '%.*s'\n", str1_encoded.len, str1_encoded.str);
+
+    Str str1_decoded = str_hex_decode_alloc(&allocator, str1_encoded);
+    printf("str1_decoded: '%.*s'\n", str1_decoded.len, str1_decoded.str);
+
+    Str str2 = S("");
+
+    Str str2_encoded = str_hex_encode_alloc(&allocator, str2);
+    printf("str2_encoded: '%.*s'\n", str2_encoded.len, str2_encoded.str);
+
+    Str str2_decoded = str_hex_decode_alloc(&allocator, str2_encoded);
+    printf("str2_decoded: '%.*s'\n", str2_decoded.len, str2_decoded.str);
+
+
+
 }
 
 int main(int argc, char *argv[])
@@ -552,6 +579,7 @@ int main(int argc, char *argv[])
     string_test_misc();
     string_test_join();
     string_test_utf8();
+    string_test_hex();
 
 }
 
diff --git a/src/string.c b/src/string.c
index 3d4d89d..a31fa5d 100644
--- a/src/string.c
+++ b/src/string.c
@@ -93,6 +93,58 @@ S64 str_index(Str haystack, Str needle)
     return -1;
 }
 
+static const char hex_chars[] = "0123456789ABCDEF";
+
+Str str_hex_encode(Str source, Str destination)
+{
+    Assert(destination.len  >= source.len * 2);
+    U32 hex_len = source.len * 2;
+    for (U32 i = 0, t = 0; i < source.len; ++i,t+=2) {
+        U8 high_nibble;
+        U8 low_nibble;
+
+        high_nibble = (source.str[i] & 0xF0) >> 4 ;
+        low_nibble =  source.str[i] & 0x0F ;
+
+        destination.str[t]   = hex_chars[high_nibble];
+        destination.str[t+1] = hex_chars[low_nibble];
+    }
+
+    destination.len = hex_len;
+    return destination;
+}
+
+Str str_hex_decode(Str source, Str destination)
+{
+    Assert(destination.len >= source.len/2);
+    U32 dest_pos = 0;
+    U32 source_pos = 0;
+
+    while (source_pos + 1 < source.len) {
+
+        if (char_is_ascii_whitespace(source.str[source_pos])) {
+            source_pos++;
+            continue;
+        }
+
+        S16 high_nibble;
+        S16 low_nibble;
+
+        high_nibble = char_hex_to_binary(source.str[source_pos]);
+        low_nibble = char_hex_to_binary(source.str[source_pos + 1]);
+        if (high_nibble == -1 || low_nibble == -1) {
+            destination.len = 0;
+            return destination;
+        }
+
+        destination.str[dest_pos] = (high_nibble << 4 ) | low_nibble;
+        source_pos += 2;
+        dest_pos++;
+    }
+
+    destination.len = dest_pos;
+    return destination;
+}
 // split @str on any byte in @separators, place split strings in @vec
 void str_split(Str str, Str separators, StrVec *vec)
 {
diff --git a/src/string.h b/src/string.h
index 0479918..6092e9b 100644
--- a/src/string.h
+++ b/src/string.h
@@ -91,7 +91,29 @@ static INLINE Str str_skip(Str str, U32 len)
     return new_str;
 }
 
+// Destination must be at least source.len * 2. Returns destination.
+Str str_hex_encode(Str source, Str destination);
+// Destination must be at least source.len / 2. Returns destination.
+Str str_hex_decode(Str source, Str destination);
 
+static INLINE Str str_hex_encode_alloc(Allocator *allocator, Str str)
+{
+    Assert(str.len <= U32_Max / 2);
+    U8 hex_len = str.len * 2;
+    U8 *result = allocator_push_array(allocator, U8, hex_len);
+    Str destination = str_create(result, hex_len);
+
+    return str_hex_encode(str, destination);
+}
+
+static INLINE Str str_hex_decode_alloc(Allocator *allocator, Str str)
+{
+    U8 binary_len = str.len / 2;
+    U8 *result = allocator_push_array(allocator, U8, binary_len);
+    Str destination = str_create(result, binary_len);
+
+    return str_hex_decode(str, destination);
+}
 // String Vector
 typedef struct StrVec StrVec;
 struct StrVec {
@@ -113,11 +135,11 @@ void str_split(Str str, Str separators, StrVec *vec);
 Str str_join(Allocator *allocator, StrVec strings, Str separator);
 
 
+// Characters
 
 static INLINE bool char_is_ascii_whitespace(U8 byte)
 {
     return byte == ' ' || byte == '\t' || byte == '\v' || byte == '\f' || byte == '\r' || byte == '\n';
-
 }
 
 static INLINE bool char_is_digit(U8 byte)
@@ -125,7 +147,17 @@ static INLINE bool char_is_digit(U8 byte)
     return byte >= '0' && byte <= '9';
 }
 
+static INLINE S16 char_hex_to_binary(U8 c)
+{
+    if (c >='0' && c <='9')
+        return c - '0';
+    else if (c >= 'A' && c <= 'F')
+        return c - 'A' + 10;
+    else if (c >= 'a' && c <= 'f')
+        return c - 'a' + 10;
 
+    return -1;
+}
 
 // UTF-8/Unicode