/*
 * minimal freestanding C library
 * 
 * works for IA-32 and Linux, uses old INT 80h software interrupts
 * for system calls.
 * 
 */

#include <stddef.h>

int strlen( char *s )
{
	char *p;
	
	p = s;
	while( *p != '\0' ) {
		p++;
	}
	
	return p - s;
}

enum {
	EXIT_SUCCESS = 0,
	EXIT_FAILURE = 1
};

enum {
	SYSCALL_EXIT = 1,
	SYSCALL_READ = 3,
	SYSCALL_WRITE = 4
};

int errno;

static __attribute__((noinline)) int syscall1( int id, int arg0 )
{
	int retval;
   
	__asm__ volatile( "\
		push %%ebx\n\
		mov %1, %%eax\n\
		mov %2, %%ebx\n\
		int $0x80\n\
		mov %%eax, %0\n\
		pop %%ebx\n" : "=m"( retval ) : "m"( id ), "m"( arg0 )
		: "eax", "ebx" );

	if( retval < 0 ) {
		errno = -retval;
		return -1;
	}

	return retval;
}

static __attribute__((noinline)) int syscall3( int id, int arg0, int arg1, int arg2 )
{
	int retval;
   
	__asm__ volatile( "\
		push %%ebx\n\
		push %%ecx\n\
		push %%edx\n\
		mov %1, %%eax\n\
		mov %2, %%ebx\n\
		mov %3, %%ecx\n\
		mov %4, %%edx\n\
		int $0x80\n\
		mov %%eax, %0\n\
		pop %%edx\n\
		pop %%ecx\n\
		pop %%ebx\n" : "=m"( retval ) : "m"( id ), "m"( arg0 ), "m"( arg1 ), "m"( arg2 )
		: "eax", "ebx", "ecx", "edx" );		

	if( retval < 0 ) {
		errno = -retval;
		return -1;
	}
	
	return retval;
}

enum {
	STDIN_FILENO = 0,
	STDOUT_FILENO = 1,
	STDERR_FILENO = 2
};

static void print_char( int fd, int c )
{
	char s[1];
	s[0] = c;
	syscall3( SYSCALL_WRITE, fd, (int)s, 1 );
}

static void print_string( char *s )
{
	syscall3( SYSCALL_WRITE, STDOUT_FILENO, (int)s, strlen( s ) );
}

static void print_newline( void )
{
	print_char( STDOUT_FILENO, '\n' );
}

static int read_string( int fd, char *buf, int size )
{
	return syscall3( SYSCALL_READ, fd, (int)buf, size );
}

enum {
	EOF = -1
};

int puts( char *s )
{
	print_string( s );
	print_newline( );
	
	return 1;
}

int getchar( )
{
	int res;
	char buf[1];
	
	res = read_string( STDIN_FILENO, buf, 1 );
	if( res == 0 ) {
		return EOF;
	}
	
	return buf[0];
}

int putchar( int c )
{
	print_char( STDOUT_FILENO, c );
	
	return c;
}

static void strreverse( char *s )
{
	char *end = s + strlen( s ) - 1;
	
	while( s < end ) {
		*s ^= *end;
		*end ^= *s;
		*s ^= *end;
		s++;
		end--;
	}
}
    
char *itoa( int v, char *s, int base )
{
	static char digit[] = "0123456789ABCDEF";
	int sign = 0;
	char *p = s;
	
	if( base < 2 || base > 16 ) {
		return NULL;
	}
	
	if( v < 0 ) {
		v = -v;
		sign = 1;
	} 
	
	do {
		*p++ = digit[v % base];
	} while( ( v /= base ) > 0 );

	if( sign ) {
		*p++ = '-';
	}
	*p = '\0';
	
	strreverse( s );
	
	return s;
}

int putint( int i )
{
	char buf[17];

	itoa( i, buf, 10 );
	print_string( buf );

	return i;
}

int putstring( char *s )
{
	print_string( s );
	
	return 0;
}

int putnl( )
{
	putchar( '\n' );
	
	return 0;
}

void exit( int status )
{
	syscall1( SYSCALL_EXIT, status );
}