Programming

int main(void)
{
        void *buffer=alloca(512);
        while(fread(stdin, 512, buffer) != NULL)
        { /* do stuff */ }
}

# like alloc, but automatic
# automatic free in return

.globl	_alloca
_alloca:
	.word	0x0000
	subl2	4(ap),sp            # crude allocation
	movl	16(fp),r1	                 # pc
	movq	8(fp),ap	         # new (old) ap and fp
	bicl2	$3,sp		         # 4-byte align
	addl2	$7*4,sp            # reuse space of mscp
	movl	sp,r0		         # return value
	jmp 	(r1)                           # funny return

malloc() took 103497088262 ns
alloca() took 135368983 ns

#include <stdlib.h>
#include <stdio.h>
#include <time.h>
#include <pthread.h>
#include <alloca.h>

#define BUFSIZE 8192
#define NUM_THR 8

static volatile int flag = 0;

typedef void ( *func_ptr )( void );

void test_malloc( void )
{
    void *ptr;
    ptr = malloc( BUFSIZE );
    free( ptr );
    return;
}

void test_alloca( void )
{
    void *ptr;
    ptr = alloca( BUFSIZE );
    return;
}

void *run( void *arg )
{
    func_ptr f;
    int ii;

    if ( flag )
        f = test_malloc;
    else
        f = test_alloca;
    for ( ii = 0; ii < ( 10 * 1024 * 1024 ); ii++ )
        f();
    return( NULL );
}

int main( int argc, char **argv )
{
    pthread_t tids[ NUM_THR ];
    hrtime_t start;
    hrtime_t end;
    void *status;
    int ii;

    flag = 1;
    start = gethrtime();
    for ( ii = 0; ii < NUM_THR; ii++ )
        pthread_create( &tids[ ii ], NULL, run, NULL );
    for ( ii = 0; ii < NUM_THR; ii++ )
        pthread_join( tids[ ii ], &status );
    end = gethrtime();
    printf( "malloc() took %lld ns\n", end - start );

    flag = 0;
    start = gethrtime();
    for ( ii = 0; ii < NUM_THR; ii++ )
        pthread_create( &tids[ ii ], NULL, run, NULL );
    for ( ii = 0; ii < NUM_THR; ii++ )
        pthread_join( tids[ ii ], &status );
    end = gethrtime();
    printf( "alloca() took %lld ns\n", end - start );
    return( 0 );
}