Path: utzoo!utgpu!news-server.csri.toronto.edu!rpi!zaphod.mps.ohio-state.edu!wuarchive!rex!uflorida!gatech!usenet.ins.cwru.edu!ncoast!dale
From: dale@NCoast.ORG (Dale Smith)
Newsgroups: comp.os.msdos.programmer
Subject: Re: alloca() for Turbo C
Message-ID: <1991Mar24.210419.24321@NCoast.ORG>
Date: 24 Mar 91 21:04:19 GMT
References: <200@esun49.nms.gdc.portal.com> <1991Mar20.054928.24101@ucselx.sdsu.edu>
Organization: North Coast Public Access Un*x (ncoast)
Lines: 134

In article <1991Mar20.054928.24101@ucselx.sdsu.edu> vaitl@ucselx.sdsu.edu (Eric Vaitl) writes:
>>Does anyone know where I can get a PD version of alloca() for Turbo C?
>>I'm trying to compile some GNU stuff which uses it.
>>
>>Thanks!
>>--
>>Jeff Chadbourne
>>chadbourne@nms.gdc.portal.com
>
>
>I got this from one of the versions of Bison floating around:
>
>/***********************************************************************\
>| The following gives the definition of a macro (alloca) that allocates |
>| space like malloc EXCEPT that it is allocated from the stack and does |
>| not have to be freed.  The allocated space will automatically disap-  |
>| pear when the function that allocated the space exits.                |
>\***********************************************************************/
>#if !defined(alloca)
>#if defined(__COMPACT__) || defined(__LARGE__) || defined(__HUGE__)
>#define alloca(i) (_SP-=((i+1)&0xFFFE),(void *)(((unsigned long)_SS<<16)|_SP))
>#else
>#define alloca(i) (_SP-=((i+1)&0xFFFE),(void *)_SP)
>#endif
>#endif


The above will trash register variables.  This one works better....

---------------- Use Ginsu knife here ---------------------
; alloca.asm
; Allocate from the stack for Turbo C 2.0
; I have not tried this with TC++ 1.0

; I got this off the net as a 386 version for unix.  I hacked it
; it fit Turbo C and non-32 bit registers.  The original was probably
; from Chip Salzenberg (if I can't spell... sorry Chip).
;    -- Dale P. Smith <dale@ncoast.org>

; void *alloca(size_t size);

; Beware of using alloca in functions without arguments
; and -k- in tiny, small, and medium models.  The stack has a
; possibility of growing.

    ifdef __TINY__
   .model   tiny
elseifdef __SMALL__
   .model   small
elseifdef __MEDIUM__
   .model   medium
elseifdef __COMPACT__
   .model   compact
elseifdef __LARGE__
   .model   large
elseifdef __HUGE__
   .model   huge
else
   .model small
endif


if @DataSize EQ 0
	.data
	extrn	___brklvl:word
endif

	.code
	public	_alloca
_alloca	proc

;; Pop return address into (es:) cx and size into ax
	pop	cx		; return address
if @CodeSize
	pop	es		; return segment
endif
	pop	ax		; size

;; Make sure that ax is greater than zero, and is a multiple of two.
	cmp	ax,0
	jl	error
	inc	ax
	and	ax,not 1

;; Figure new stack pointer, check for negative and less than brk.
	mov	bx,sp
	sub	bx,ax
	jb	error		; below zero
if @DataSize EQ 0		; tiny, small, medium
	cmp	bx,___brklvl
	jb	error		; below the brk
endif
	xchg	sp,bx
	mov	ax,sp


;; Copy the (hypothetical) register variables.
ifdef __MEDIUM__
	push	ss:6[bx]	; return segment(medium)
endif
	push	ss:4[bx]	; return offset(med,sm,tiny) or ds(huge)
	push	ss:2[bx]	; di (all)
	push	ss:[bx]		; si (all)

if @DataSize
	mov	dx,ss
endif

exit:
;; Put something on the stack so that our caller can pop it off.
	push	ax

;; Return to the the caller.
if @CodeSize
	push	es
	push	cx
	ret
else
	jmp	cx
endif

error:
	xor	ax,ax
if @DataSize
	cwd
endif
	jmp	exit

	endp
	end
-- 
 Dale P. Smith
 dale@ncoast.org                         dale@harco3.uucp
 uunet!usenet.ins.cwru.edu!ncoast!dale   uunet!aablue!fmsystm!harco3!dale