Path: utzoo!utgpu!water!watmath!clyde!ima!cfisun!lakart!dg
From: dg@lakart.UUCP (David Goodenough)
Newsgroups: comp.sources.d
Subject: Re: Simulation of 'alloca' -- can it be done in TurboC or MSC?
Message-ID: <134@lakart.UUCP>
Date: 23 May 88 23:22:23 GMT
References: <203@lcuxa.UUCP>
Organization: Lake - The systems people
Lines: 32

From article <203@lcuxa.UUCP>, by mike2@lcuxa.UUCP (M S Slomin):
> Quick question: has anyone worked out a way to simulate the 'alloca'
> function in either TurboC or MSC (DOS for those who don't know)?

Write it in assembler. I don't know how to do alloca in C in a portable
manner. Come to that - since you have to mess with your frame/stack pointer
I don't think it can be done in anything other than assembler. Sure can't
on a z80.

CAVEAT for my z80 implementetion, you are advised NOT TO USE in a complex
expression (where temp results need to be stacked)  think about it!!

.extern	_alloca
_alloca:
	pop	de
	pop	hl
	call	#neg			; negate argument
	add	hl,sp			; allocate the space
	push	hl
	push	de			; put args back so return works
	ret				; home we go - hl points to space.

This should be fairly easy to convert to 8086 assembler (What, your C compiler
can't talk in assembler?? :-) Different segments may be a pain - this space
will be in SS:, and I can just see referencing through a 16 bit pointer as DS:
UGH!!. Still if you send back a 32 bit pointer SEG:OFFSET or make sure
DS: and SS: are the same, you should be flying.
-- 
	dg@lakart.UUCP - David Goodenough		+---+
							| +-+-+
	....... !harvard!adelie!cfisun!lakart!dg	+-+-+ |
						  	  +---+