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+# Copyright(c) 1986 Association of Universities for Research in Astronomy Inc.
+
+include	<syserr.h>
+include	<knet.h>
+include	"environ.h"
+
+.help environ
+.nf ___________________________________________________________________________
+ENVIRON -- Routines for managing the environment list.  The environment list
+is global in scope.  A process, e.g., the CL, builds up the environment list
+and passes it on to a child process when the process is spawned.
+
+       nchars = envgets (name, value, maxch)	# get value of envvar
+	redef =	envputs (name, value)		# set value of envvar
+       nchars = envfind (name, value, maxch)	# get value of envvar if def
+		envmark (sp)			# mark stack pointer
+      nredefs = envfree (sp, userfcn)		# free back to marked posn
+
+	 bool = envgetb (name)			# get boolean value of envvar
+	  int = envgeti (name)			# get integer value of envvar
+		envlist (fd, prefix, show_redefs)	# print envlist on file
+	nscan =	envscan (input_source)		# read SET stmts from a file
+
+	 el = env_first (valp)			# head of envlist
+	  el = env_next (el, valp, show_redefs) # next element of envlist
+
+The environment list is maintained as a multi-threaded linked list.  This
+provides the searching efficiency of a hash table plus stack like semantics
+for redefinitions and for freeing blocks of variables.  There are two primary
+data structures internally, an array of pointers to the heads of the threads,
+and a buffer containing the list elements.  These data structures are
+dynamically allocated and will be automatically reallocated at runtime if
+overflow occurs.  The number of threads determines the hashing efficiency and
+is a compile time parameter.
+
+The ENVMARK and ENVFREE procedures mark and free storage on the environment
+list stack.  All environment variables defined or redefined after a call to
+ENVMARK will be deleted and storage freed by a call to ENVFREE.  If a redef
+is freed the next most recent definition becomes current.  ENVFREE returns
+as its function value the number of redefined variables uncovered by the free
+operation.  The calling program must mark and free in the correct order or the
+environment list may be trashed.
+
+The ENVLIST procedure prints the environment list on a file.  Redefined values
+will only be printed if desired.  The environment list is printed as a list of
+SET statements in most recent first order, i.e.,
+
+	set nameN=valueN
+	set nameM=valueM
+	    ...
+	set name1=value1
+
+The ENVLIST function is used both to inspect the environment list and to pass
+the list on to a child process.  Redefined variables are omitted when passing
+the list on to a child process, hence the order of definition does not matter.
+The output format is "prefix name=value", where the prefix string is supplied
+by the user.
+
+The ENVSCAN function parses one or more SET statements, calling ENVPUTS to
+enter the SET declarations into the environment list.  The argument is either
+a SET declaration or a string of the form "set @filename", where "filename" is
+the name of a file containing set declarations.
+.endhelp ______________________________________________________________________
+
+
+# ENVFIND -- Search the environment list for the named environment variable
+# and return the string value if found.
+
+int procedure envfind (key, value, maxch)
+
+char	key[ARB]		# environment variable name
+char	value[maxch]		# string value (output)
+int	maxch
+
+long	sum
+pointer	el, ep
+int	head, ip, nchars
+int	envputs(), gstrcpy()
+include	"environ.com"
+
+begin
+	# Get index into envbuf of the first element of the thread.
+	if (key[1] == EOS)
+	    head = NULL
+	else {
+	    sum = 0
+	    do ip = 1, MAX_HASHCHARS {
+		if (key[ip] == EOS)
+		    break
+		sum = sum + (sum + key[ip])
+	    }
+	    head = threads[mod(sum,NTHREADS)+1]
+	}
+
+	# If thread is not empty search down it for the named key and return
+	# the value string if found.  Note that the value of the E_NEXT pointer
+	# is given as an integer offset into envbuf to facilitate reallocation
+	# upon overflow.
+
+	if (head != NULL)
+	    for (el = envbuf + head;  el > envbuf;  el = envbuf + E_NEXT(el)) {
+		ep = E_SETP(el)
+		for (ip=1;  key[ip] == Memc[ep];  ip=ip+1)
+		    ep = ep + 1
+		if (key[ip] == EOS && Memc[ep] == '=')
+		    return (gstrcpy (Memc[ep+1], value, maxch))
+	    }
+
+	# Key not found.  Ask the host system for the value of the environment
+	# variable.
+
+	call strpak (key, value, maxch)
+	call zgtenv (value, value, maxch, nchars)
+
+	if (nchars >= 0)  {
+	    call strupk (value, value, maxch)
+	    ip = envputs (key, value)
+	    return (nchars)
+	} else {
+	    value[1] = EOS
+	    return (ERR)
+	}
+end
+
+
+# ENVPUTS -- Add a new SET definition to the environment list.  A SET operation
+# is allowed to redefine a previously defined environment variable, but if the
+# new definition is a redef we return YES as the function value.  If the set
+# is a no-op (null key, or redef with the same value as previously) the envlist
+# is not modified and NO is returned as the function value.
+
+int procedure envputs (key, value)
+
+char	key[ARB]		# environment variable name
+char	value[ARB]		# string value
+
+long	sum
+int	head, thread_index, redef, ip
+pointer	el, op, ep
+
+bool	streq()
+pointer	coerce()
+int	gstrcpy(), krealloc()
+include	"environ.com"
+
+begin
+	if (key[1] == EOS)
+	    return (NO)
+
+	# Get index into envbuf of the first element of the thread.
+	sum = 0
+	do ip = 1, MAX_HASHCHARS {
+	    if (key[ip] == EOS)
+		break
+	    sum = sum + (sum + key[ip])
+	}
+
+	thread_index = mod (sum, NTHREADS) + 1
+	head = threads[thread_index]
+
+	# If thread is not empty search down it for the named key to see if we
+	# have a redefinition.  If we have a redef but the new value is the
+	# same as the old, do nothing.  Otherwise flag the element being
+	# redefined as a redefinition (so that ENVLIST can ignore it).
+
+	redef = NO
+	if (head != NULL)
+	    for (el = envbuf + head;  el > envbuf;  el = envbuf + E_NEXT(el)) {
+		ep = E_SETP(el)
+		for (ip=1;  key[ip] == Memc[ep];  ip=ip+1)
+		    ep = ep + 1
+		if (key[ip] == EOS && Memc[ep] == '=')
+		    if (streq (Memc[ep+1], value))
+			return (NO)
+		    else {
+			E_REDEF(el) = YES
+			redef = YES
+			break
+		    }
+	    }
+
+	# Append the new list element to the end of ENVBUF, increasing the size
+	# of the buffer if overflow occurs.  The list structure must be aligned
+	# on a short integer boundary.  Set the back link pointers for searches.
+
+	if (top + MAX_LENLISTELEM >= len_envbuf) {
+	    len_envbuf = len_envbuf + INC_ENVBUF
+	    if (krealloc (envbuf, len_envbuf, TY_SHORT) == ERR)
+		call sys_panic (SYS_MFULL, "Out of memory")
+	}
+
+	el = envbuf + top
+	E_NEXT(el)     = head
+	E_LASTELEM(el) = last
+	E_REDEF(el)    = NO
+
+	# Deposit the string "key=value" in the E_SET field.  At least
+	# MIN_SZVALUE chars are allocated for the value string, to permit
+	# the value to be updated via ENVRESET (possibly changing size in
+	# the process).
+
+	op = E_SETP(el)
+	op = op + gstrcpy (key, Memc[op], MAX_SZKEY)
+	Memc[op] = '='
+	op = op + 1
+	E_LEN(el) = max (MIN_SZVALUE, gstrcpy(value,Memc[op],MAX_SZVALUE))
+	op = op + E_LEN(el) + 1
+
+	last = top
+	threads[thread_index] = last
+	top = coerce (op, TY_CHAR, TY_SHORT) - envbuf
+
+	# Update the environment in any connected kernel servers.
+	call ki_envreset (key, value)
+
+	return (redef)
+end
+
+
+# ENVMARK -- Mark the position in the environment list.  A subsequent call
+# to ENVFREE with the marked position as argument will unset all elements
+# set after the marked position.
+
+procedure envmark (old_top)
+
+int	old_top			# top of envbuf stack
+include	"environ.com"
+
+begin
+	old_top = top
+end
+
+
+# ENVFREE -- Free all environment list entries set since the matching call
+# to ENVMARK.  Return as the function value the number of redefined environment
+# variables uncovered by the free operation.  If the ZLOCPR integer entry point
+# address of the user supplied function USERFCN is nonnull the function will
+# be called with the name and value of each uncovered redefinition.  The calling
+# sequence is as follows:  subroutine userfcn (name, value)
+
+int procedure envfree (old_top, userfcn)
+
+int	old_top			# top of envbuf stack
+int	userfcn			# epa of function called for uncovered redefs
+
+int	nredefs, head, i, j, t
+pointer	sp, start, namep, el1, el2, ep1, ep2
+include	"environ.com"
+
+begin
+	if (old_top < 1 || old_top >= top)
+	    return (0)
+
+	call smark (sp)
+	call salloc (namep, SZ_FNAME, TY_CHAR)
+
+	nredefs = 0
+
+	# Clear the redef flags for all list elements that are redefined by
+	# elements above the new top, and count the number of uncovered redefs.
+	# Examine only non-empty threads.
+
+	for (t=1;  t <= NTHREADS;  t=t+1) {
+	    head = threads[t]
+	    if (head != NULL) {
+		# Examine only list elements in the thread which lie above the
+		# top we are reverting to.
+
+		for (j = head;  j >= old_top;  j = E_NEXT(el1)) {
+		    el1 = envbuf + j
+
+		    # Scan down the thread to see if this is a redefinition,
+		    # and clear the redef flag if so.
+
+		    for (i = j;  i != NULL;  i = E_NEXT(el2)) {
+			el2 = envbuf + i
+			if (E_REDEF(el2) == YES) {
+			    ep1 = E_SETP(el1)
+			    ep2 = E_SETP(el2)
+			    start = ep2
+			    while (Memc[ep1] == Memc[ep2] && Memc[ep1] != '=') {
+				ep1 = ep1 + 1
+				ep2 = ep2 + 1
+			    }
+			    if (Memc[ep1] == '=') {
+				E_REDEF(el2) = NO
+				nredefs = nredefs + 1
+				if (userfcn != NULL) {
+				    call strcpy (Memc[start], Memc[namep],
+					ep2 - start)
+				    call zcall2 (userfcn,
+					Memc[namep], Memc[ep2+1])
+				}
+				break
+			    }
+			}
+		    }
+		}
+
+		# Set the head of the thread to the first element below
+		# the new top.
+
+		threads[t] = j
+	    }
+	}
+
+	# The variable OLD_TOP is the index of a list element.  Make it the
+	# new top.
+
+	top = old_top
+	last = E_LASTELEM(envbuf+top)
+
+	call sfree (sp)
+	return (nredefs)
+end