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map: use starting character lists for keys[]

--- a/map.c

+++ b/map.c

@@ -2,20 +2,36 @@

 #include <string.h>

 #include "roff.h"

+/* register, macro, or environments names with more than two characters */

 static char keys[NREGS][GNLEN];

-static int nkeys;

+static int nkeys = 1;

+/* per starting character name lists */

+static int key_head[256];

+static int key_next[NREGS];

+/* return the index of s in keys[]; insert it if not in keys[] */

+static int key_get(char *s)

+{

+	int head = (unsigned char) s[0];

+	int i = key_head[head];

+	while (i > 0) {

+		if (!strcmp(keys[i], s))

+			return i;

+		i = key_next[i];

+	}

+	i = nkeys++;

+	strcpy(keys[i], s);

+	key_next[i] = key_head[head];

+	key_head[head] = i;

+	return i;

+}

+

 /* map register names to [0..NREGS * 2) */

 int map(char *s)

 {

-	int i;

 	if (n_cp || !s[1] || !s[2])

 		return REG(s[0], s[1]);

-	for (i = 0; i < nkeys; i++)

-		if (keys[i][0] == s[0] && !strcmp(keys[i], s))

-			return NREGS + i;

-	strcpy(keys[nkeys++], s);

-	return NREGS + nkeys - 1;

+	return NREGS + key_get(s);

 }

 /* returns a static buffer */