1 files changed, 74 insertions, 0 deletions
diff --git a/sys/symtab/stfind.x b/sys/symtab/stfind.x
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+++ b/sys/symtab/stfind.x
@@ -0,0 +1,74 @@
+# Copyright(c) 1986 Association of Universities for Research in Astronomy Inc.
+
+include	"symtab.h"
+
+# STFIND -- Search the symbol table for the named key and return a pointer to
+# the symstruct or NULL.  This is the main table lookup procedure.  If the
+# thread is empty NULL is returned after only a hash function call.  If there
+# is only one element on a thread (common for well conditioned symbol tables)
+# the expense is essentialy two traversals of the key string plus procedure
+# overhead (pointer calculations, etc.).
+
+pointer procedure stfind (stp, key)
+
+pointer	stp			# symbol table descriptor
+char	key[ARB]		# symbol name
+
+long	sum
+char	first_char
+int	head, ip, thread
+pointer	el, cp, stab, sbuf
+
+begin
+	# When a symbol is entered in the table a flag is set in the ST_ASCII
+	# array to flag that the symbol table contains at least one key
+	# beginning with that character.  If the flag is not set we can thus
+	# determine very quickly that the symbol is not present.  This is
+	# important for applications such as mapping identifiers for macro
+	# expansion, where most macros have upper case keys but most program
+	# identifiers have lower case keys.  (Subtle note: since the first
+	# element of ST_ASCII is for ascii value 0=EOS, the following also
+	# serves to detect null keys).
+
+	if (ST_ASCII(stp,key[1]) == 0)
+	    return (NULL)
+
+	# Hash the key onto a thread in the index.
+	sum = 0
+	do ip = 1, MAX_HASHCHARS {
+	    if (key[ip] == EOS)
+		break
+	    sum = sum + (sum + key[ip])
+	}
+
+	thread = mod (sum, ST_INDEXLEN(stp))
+	head = Memi[ST_INDEX(stp)+thread]
+
+	# If thread is not empty search down it for the named key and return
+	# the symbol pointer if found.  Note that the value of the E_NEXTHASH
+	# pointer is given as an integer offset to facilitate reallocation
+	# upon overflow.
+
+	if (head != NULL) {
+	    first_char = key[1]
+	    sbuf = ST_SBUFP(stp)
+	    stab = ST_STABP(stp)
+
+	    for (el=stab+head;  el > stab;  el=stab+E_NEXTHASH(el)) {
+		cp = sbuf + E_KEY(el)
+		if (Memc[cp] != first_char)
+		    next
+
+		# Compare target key to symbol key.
+		do ip = 1, MAX_SZKEY {
+		    if (key[ip] != Memc[cp])
+			break
+		    if (key[ip] == EOS)
+			return (E_USERFIELDS(el))	# found key
+		    cp = cp + 1
+		}
+	    }
+	}
+
+	return (NULL)
+end