torch@attctc.Dallas.TX.US (Jay Finger) (02/09/90)
About a week ago I requested a copy of alloca for Think C 4.0. I received
several descriptions of what alloca is supposed to do, along with the version
of alloca in Earle Horton's port of bison to MPW. I also received several
requests for whatever I came up with, so here it is.
The alloca function below is completely inline: it uses a few more words
of memory that way, but since it's inline it doesn't have to jack with
the return address or stack frame (from what I've seen ThinkC always
puts a LINK instruction at the beginning of the function, even if it's
all in assembler and you've got no local variables).
I was rather suprised to discover that inline functions must be pascal
style functions; a C function would have been better because the
return value would be passed back in D0 instead of on the stack.
Anyhow, here's the declaration for alloca. You'll probable want to put
in a file called "alloca.h" somewhere. I've got bison (not the MPW
version; version 1.03 (8/23/89) from osu-cis) up and running after about
ten hours of work. I haven't tested it with anything big yet, but this
alloca isn't breaking it.
---------------------- cut here --------------------------------------
pascal void *alloca(long size) =
{
0x201F, /* MOVE.L (SP)+,D0 ;get size */
0x5680, /* ADDQ.L #3,D0 ;make it a multiple of 4 */
0x0240, 0xFFFC, /* ANDI.W #-4,D0 */
0x9FC0, /* SUB.L D0,SP ;allocate it */
0x2F0F /* MOVE.L SP,-(SP) ;return value on stack */
};
----------------------------------------------------------------------
Jay Finger,
{ames,mit-eddie}!attctc!torch
ames!torch@attctc