From d370ab57b97f352ace48992a01dc57ad84d57dd0 Mon Sep 17 00:00:00 2001
From: Nick Bowler <nbowler@draconx.ca>
Date: Tue, 20 Feb 2024 20:52:04 -0500
Subject: [PATCH] copysym: Integrate code offset into lookup table.

Instead of shifting out a nibble from a 64-bit constant based on the
lookup result, we can just add a byte to each entry in the table with
the same value.  Since we no longer need to worry about fitting the
offsets into 4 bits we can also rearrange the code array a bit, for
an overall code size reduction.
---
 src/copysym.c | 104 +++++++++++++++++++++++---------------------------
 1 file changed, 48 insertions(+), 56 deletions(-)

diff --git a/src/copysym.c b/src/copysym.c
index 3128c3e..ca23c44 100644
--- a/src/copysym.c
+++ b/src/copysym.c
@@ -16,11 +16,11 @@
 
 #include <stdlib.h>
 #include <string.h>
+#include <stddef.h>
 
 #if HAVE_INTTYPES_H
 #include <inttypes.h>
 typedef uint_least32_t dx_u32;
-typedef uint_least64_t dx_u64;
 #else
 #include <limits.h>
 #if UINT_MAX >= 0xffffffff
@@ -28,16 +28,18 @@ typedef unsigned dx_u32;
 #else
 typedef unsigned long dx_u32;
 #endif
-typedef unsigned long long dx_u64;
 #endif
 
-#define ARRAYSIZE(x) (sizeof (x) / sizeof (x)[0])
+#define BSEARCH_ARRAY(key, arr, cmp) \
+	bsearch(key, arr, sizeof (arr) / sizeof *(arr), sizeof *(arr), cmp)
 
-static int compar_5arr(const void *key, const void *elem_)
+enum { PREFIXLEN = 5 };
+
+static int compar_prefix(const void *key, const void *elem_)
 {
-	const char (*elem)[5] = (void *)elem_;
+	const char (*elem)[PREFIXLEN+1] = (void *)elem_;
 
-	return strncmp(key, *elem, sizeof *elem);
+	return strncmp(key, *elem, PREFIXLEN);
 }
 
 /*
@@ -92,14 +94,14 @@ const char *copyright_symbol(const char *charset)
 {
 	/* All known encodings of the copyright symbol */
 	static const char codes[] =
-		"\xc2\xa9"         "\0"
-		"\x97"             "\0"
-		"\xa8"             "\0"
-		"\xb8"             "\0"
-		"\xbf"             "\0"
-		"\x8f\xa2\xed"     "\0"
-		"\x81\x30\x84\x38" "\0"
-		"(C)";
+		"(C)"          "\0"
+		"\xc2\xa9"     "\0"
+		"\x97"         "\0"
+		"\xa8"         "\0"
+		"\xb8"         "\0"
+		"\xbf"         "\0"
+		"\x8f\xa2\xed" "\0"
+		"\x81\x30\x84\x38";
 
 	/*
 	 * We need the list below to be in lexicographic order in
@@ -113,44 +115,38 @@ const char *copyright_symbol(const char *charset)
 	 * For character sets that include the copyright symbol,
 	 * the first 5 characters suffices to distinguish amongst
 	 * all the different possible encodings.
+	 *
+	 * The final byte of each entry indicates the corresponding
+	 * offset into the codes array, except for CP112x and ISO-8859-x
+	 * which use the special values 0 and 1, respectively (handled
+	 * below).
 	 */
-	static const char t1[][5] = {
-		"CP112",
-		"CP125",
-		"CP775",
-		"CP850",
-		"CP856",
-		"CP857",
-		"CP869",
-		"CP922",
-		"EUC-J",
-		"GB180",
-		"GEORG",
-		"ISO-8",
-		"KOI8-",
-		"PT154",
-		"UTF-8"
+	static const char t1[][PREFIXLEN+1] = {
+		"CP112\x00",
+		"CP125\x05",
+		"CP775\x09",
+		"CP850\x0b",
+		"CP856\x0b",
+		"CP857\x0b",
+		"CP869\x07",
+		"CP922\x05",
+		"EUC-J\x0f",
+		"GB180\x13",
+		"GEORG\x05",
+		"ISO-8\x01",
+		"KOI8-\x0d",
+		"PT154\x05",
+		"UTF-8\x04"
 	};
 
-	/*
-	 * Each nibble in the results value contains the offset in the
-	 * codes array for the corresponding index in t1, except that
-	 * ISO-8859 matches the special value '2' (handled below).
-	 */
-	dx_u64 results = 0x001921fb13777511ull;
-	const char (*m1)[sizeof *t1];
-	unsigned x, cindex;
-
-	if (!charset)
-		goto no_conv;
+	unsigned cindex = 0;
+	const char *m;
 
-	m1 = bsearch(charset, t1, ARRAYSIZE(t1), sizeof *t1, compar_5arr);
-	if (!m1)
+	if (!charset || !(m = BSEARCH_ARRAY(charset, t1, compar_prefix)))
 		goto no_conv;
-	charset += 5;
 
-	x = m1-t1;
-	cindex = (results >> (x << 2)) & 0xf;
+	cindex = m[PREFIXLEN];
+	charset += PREFIXLEN;
 
 	/*
 	 * We now need to identify encodings that match one of the 5-character
@@ -168,10 +164,10 @@ const char *copyright_symbol(const char *charset)
 	 *   ISO-8859-5
 	 *   ISO-8859-6
 	 */
-	if ((x == 0) != (*charset == '9')) {
-		/* CP112x, x != '9', no copyright symbol. */
-		goto no_conv;
-	} else if (cindex == 2) {
+	if (cindex == 0) {
+		/* CP112x, only CP1129 has copyright symbol. */
+		cindex = 5 * (*charset == '9');
+	} else if (cindex == 1) {
 		/*
 		 * ISO-8859 special case.  Simply find and look at the final
 		 * two digits.  The set bits in the 'accept' value indicate
@@ -188,14 +184,10 @@ const char *copyright_symbol(const char *charset)
 				collect |= c - '0';
 		}
 
-		cindex = (accept >> (collect & 0x1f)) & 1;
-		if (!cindex)
-			goto no_conv;
+		cindex = 5 * ((accept >> (collect & 0x1f)) & 1);
 	}
-
-	return &codes[cindex];
 no_conv:
-	return &codes[20];
+	return codes+cindex;
 }
 
 #endif
-- 
2.43.2