.\" $NetBSD: STACK.9,v 1.2 2011/04/08 07:55:04 jruoho Exp $
.\"
.\" Copyright (c) 2010 The NetBSD Foundation, Inc.
.\" All rights reserved.
.\"
.\" This code is derived from software contributed to The NetBSD Foundation
.\" by Jukka Ruohonen.
.\"
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" 1. Redistributions of source code must retain the above copyright
.\"    notice, this list of conditions and the following disclaimer.
.\" 2. Redistributions in binary form must reproduce the above copyright
.\"    notice, this list of conditions and the following disclaimer in the
.\"    documentation and/or other materials provided with the distribution.
.\"
.\" THIS SOFTWARE IS PROVIDED BY THE NETBSD FOUNDATION, INC. AND CONTRIBUTORS
.\" ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED
.\" TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR
.\" PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE FOUNDATION OR CONTRIBUTORS
.\" BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR
.\" CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF
.\" SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
.\" INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
.\" CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
.\" ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
.\" POSSIBILITY OF SUCH DAMAGE.
.\"
.Dd April 8, 2011
.Dt STACK 9
.Os
.Sh NAME
.Nm STACK
.Nd stack macros
.Sh SYNOPSIS
.In sys/param.h
.Ft type
.Fn STACK_ALLOC "sp" "size"
.Ft type
.Fn STACK_MAX "sp" "size"
.Ft type
.Fn STACK_ALIGN "sp" "bytes"
.Ft type
.Fn STACK_GROW "sp" "size"
.Ft type
.Fn STACK_SHRINK "sp" "size"
.Sh DESCRIPTION
A stack is an area of memory with a fixed origin but with a variable size.
A stack pointer points to the most recently referenced location on the stack.
Initially, when the stack has a size of zero,
the stack pointer points to the origin of the stack.
When data items are added to the stack,
the stack pointer moves away from the origin.
.Pp
The
.Fn STACK_ALLOC
macro returns a pointer to allocated stack space of some
.Fa size .
Given the returned pointer
.Fa sp
and
.Fa size ,
.Fn STACK_MAX
returns the maximum stack address of the allocated stack space.
The
.Fn STACK_ALIGN
macro can be used to align the stack pointer
.Fa sp
by the specified amount of
.Fa bytes .
.Pp
Two basic operations are common to all stacks:
a data item is added
.Pq Dq push
to the location pointed by
.Fa sp
or a data item is removed
.Pq Dq pop
from the stack.
The stack pointer must be subsequently adjusted by the size of the data item.
The
.Fn STACK_GROW
and
.Fn STACK_SHRINK
macros adjust the stack pointer
.Fa sp
by given
.Fa size .
.Pp
A stack may grow either up or down.
The described macros take this into account by using the
.Dv __MACHINE_STACK_GROWS_UP
preprocessor define.
.Sh SEE ALSO
.Xr param 3 ,
.Xr queue 3