some optimization for hex_decode()

src/hex.c

@@ -28,6 +28,7 @@
 
 #include <ctype.h>
 #include <errno.h>
+#include <stdint.h>
 
 #include "vmod_convert.h"
 
@@ -39,7 +40,19 @@ static const char hex_alphabet[][16] = {
 	"0123456789ABCDEF"
 };
 
-static char nibble[128];
+/*
+ * Shift the ASCII table over so that it begins at '0', and replace the
+ * hex digits with their binary values. This fits all of the hex digits
+ * into 54 bytes (cacheline friendly).
+ */
+static const uint8_t nibble[] = {
+	   0,    1,    2,    3,    4,    5,    6,    7,    8,    9,
+	   0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 10,   11,   12,
+	   13,   14,   15,   0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+	   0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff,
+	   0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 0xff, 10,   11,
+	   12,   13,   14,   15
+};
 
 static inline int
 isxstr(const char * const p, ssize_t *l)
@@ -75,6 +88,12 @@ check(const char * const p, va_list ap)
 	return len;
 }
 
+static inline char
+hex2byte(const unsigned char hi, const unsigned char lo)
+{
+	return (nibble[hi - '0'] << 4) | nibble[lo - '0'];
+}
+
 static inline void
 decode_str(const char *restrict const p, char *restrict *restrict dest,
 	   unsigned char *restrict extranib)
@@ -83,28 +102,15 @@ decode_str(const char *restrict const p, char *restrict *restrict dest,
 	char *d = *dest;
 
 	if (*extranib)
-		*d++ = (nibble[*extranib] << 4) | nibble[*s++];
+		*d++ = hex2byte(*extranib, *s++);
 	while (*s && *(s+1)) {
-		*d++ = (nibble[*s] << 4) | nibble[*(s+1)];
+		*d++ = hex2byte(*s, *(s+1));
 		s += 2;
 	}
 	*extranib = *s;
 	*dest += d - *dest;
 }
 
-void
-hex_init(void)
-{
-	for (int i = 0; i < 128; i++)
-		nibble[i] = -1;
-	for (char c = '0'; c <= '9'; c++)
-		nibble[(int) c] = c - '0';
-	for (char c = 'a'; c <= 'f'; c++)
-		nibble[(int) c] = c - 'a' + 10;
-	for (char c = 'A'; c <= 'F'; c++)
-		nibble[(int) c] = c - 'A' + 10;
-}
-
 ssize_t
 hex_encode(const enum encoding enc, char *restrict const buf,
 	   const size_t maxlen, const char *restrict const in,

src/vmod_convert.c

@@ -151,7 +151,6 @@ event(VRT_CTX, struct vmod_priv *priv, enum vcl_event_e event)
 	if (event != VCL_EVENT_LOAD)
 		return 0;
 
-	hex_init();
 	base64_init();
 	return (0);
 }

src/vmod_convert.h

@@ -109,6 +109,5 @@ void base64_init(void);
 encode_f base64_encode;
 
 /* hex.c */
-void hex_init(void);
 encode_f hex_encode;
 decode_f hex_decode;