[vvhitespace] / vv_interpreter.c

/*
 * (c) 2019 Aaron Taylor <ataylor at subgeniuskitty dot com>
 * All rights reserved.
 */

#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <string.h>
#include <errno.h>
#include <stdint.h>
#include <sys/select.h>
#include <getopt.h>
#include <termios.h>

#define VERSION 1

#define HEAPSIZE        1024    /* Size of heap in words        */
#define DATASTACKSIZE   1024    /* Size of stack in words       */
#define RETURNSTACKSIZE 1024    /* Max subroutine call depth    */

void
print_usage(char ** argv)
{
    printf( "VVhitespace Interpreter v%d (www.subgeniuskitty.com)\n"
            "Usage: %s -i <file>\n"
            "  -h         Help (prints this message)\n"
            "  -i <file>  Specify a VVhitespace source file to interpret.\n"
            , VERSION, argv[0]
    );
}

int
stdin_empty(void)
{
    fd_set read_fds;
    FD_ZERO(&read_fds);
    FD_SET(STDIN_FILENO, &read_fds);

    struct timeval timeout;
    timeout.tv_sec = 0;
    timeout.tv_usec = 0;

    int retval = select(1, &read_fds, NULL, NULL, &timeout);
    /* retval could be -1. Ignoring that for now. */
    if (retval > 0) return 0;
    return 1;
}

void
set_terminal_mode(void)
{
    struct termios options;
    tcgetattr(STDIN_FILENO, &options);
    /* Create a cbreak-like environment through the following options. */
    options.c_lflag &= ~ECHO; /* Disable echoing of input characters. */
    options.c_lflag &= ~ICANON; /* Disable cooked/line-oriented mode. */
    options.c_cc[VMIN] = 1;
    options.c_cc[VTIME] = 0;
    tcsetattr(STDIN_FILENO, TCSANOW, &options);
}

void
unset_terminal_mode(void)
{
    struct termios options;
    tcgetattr(STDIN_FILENO, &options);
    /* Undo the changes made in set_terminal_mode(). */
    options.c_lflag |= ECHO; /* Enable echoing of input characters. */
    options.c_lflag |= ICANON; /* Enable cooked/line-oriented mode. */
    options.c_cc[VMIN] = 1; /* Default value from /usr/src/sys/sys/ttydefaults.h */
    options.c_cc[VTIME] = 0; /* Default value from /usr/src/sys/sys/ttydefaults.h */
    tcsetattr(STDIN_FILENO, TCSANOW, &options);
}

void
ws_die(size_t * pc, char * msg)
{
    printf("SIM_ERROR @ PC %lu: %s\n", *pc, msg);
    fflush(stdout);
    unset_terminal_mode();
    exit(EXIT_FAILURE);
}

void
stack_push(int64_t ** sp, int64_t word)
{
    *((*sp)++) = word;
}

int64_t
stack_pop(int64_t ** sp)
{
    return *(--(*sp));
}

int64_t
stack_peek(int64_t ** sp, size_t offset)
/* offset=0 peeks TOS, offset=1 peeks NOS, etc. */
{
    return *((*sp)-offset-1);
}

uint8_t
next_code_byte(uint8_t * code, size_t * pc)
{
    return code[(*pc)++];
}

/*
 * In addition to returning the parsed label, this function advances the PC to
 * the next instruction.
 */
uint16_t
parse_label(uint8_t * code, size_t * pc)
{
    uint16_t label = 0;
    uint8_t c;
    while ((c = code[(*pc)++]) != '\n') {
        label = label << 1;
        if (c == ' ') label++;
    }
    // TODO: Where should I handle attempts to access an unitialized label?
    //       For now, leave it undefined in a nasal demon sense.
    return label;
}

void
populate_labels(size_t * labels, uint8_t * code, size_t code_size)
{
    size_t cp = 0;
    while (cp <= code_size) {
        if (code[cp] == '\v') {
            uint16_t temp_label = parse_label(code, &cp);
            labels[temp_label] = cp;
        }
        cp++;
    }
}

void
process_imp_stack(uint8_t * code, size_t * pc, int64_t ** sp)
{
    switch (next_code_byte(code,pc)) {
        case ' ':
            /* Push number onto TOS. */
            {
                /* First, pick off the sign */
                int64_t sign = 0;
                switch (next_code_byte(code,pc)) {
                    case ' ' :  sign = 1;                       break;
                    case '\t':  sign = -1;                      break;
                    default  :  ws_die(pc, "expected sign");    break;
                }

                /* Now, construct the number and push to TOS. */
                /* I'm assuming the numbers are read MSb first. */
                int64_t number = 0;
                uint8_t temp;
                while ((temp = next_code_byte(code,pc)) != '\n') {
                    if (temp == '\v') ws_die(pc, "non-binary digit in number");
                    number <<= 1;
                    if (temp == '\t') number++;
                }
                stack_push(sp, number*sign);
            }
            break;
        case '\n':
            /* Stack sub-command */
            {
                switch (next_code_byte(code,pc)) {
                        /* Duplicate the TOS. */
                    case ' ':
                        stack_push(sp, stack_peek(sp,0));
                        break;
                        /* Swap TOS and NOS. */
                    case '\t':
                        {
                            int64_t t1 = stack_pop(sp);
                            int64_t t2 = stack_pop(sp);
                            stack_push(sp, t1);
                            stack_push(sp, t2);
                        }
                        break;
                        /* Discard TOS. */
                    case '\n':
                        stack_pop(sp);
                        break;
                    default:
                        ws_die(pc, "malformed stack IMP");
                        break;
                }
            }
            break;
        default: ws_die(pc, "malformed stack IMP"); break;
    }
}

void
process_imp_arithmetic(uint8_t * code, size_t * pc, int64_t ** sp)
{
    int64_t temp;
    switch (next_code_byte(code,pc)) {
        case ' ':
            {
                switch (next_code_byte(code,pc)) {
                    case ' ':
                        /* Addition */
                        stack_push(sp, stack_pop(sp)+stack_pop(sp));
                        break;
                    case '\t':
                        /* Subtraction */
                        temp = stack_pop(sp);
                        stack_push(sp, stack_pop(sp)-temp);
                        break;
                    case '\n':
                        /* Multiplication */
                        stack_push(sp, stack_pop(sp)*stack_pop(sp));
                        break;
                    default:
                        ws_die(pc, "malformed arithmetic IMP");
                        break;
                }
            }
            break;
        case '\t':
            {
                switch (next_code_byte(code,pc)) {
                    case ' ':
                        /* Division */
                        temp = stack_pop(sp);
                        stack_push(sp, stack_pop(sp)/temp);
                        break;
                    case '\t':
                        /* Modulo */
                        temp = stack_pop(sp);
                        stack_push(sp, stack_pop(sp)%temp);
                        break;
                    default: ws_die(pc, "malformed arithmetic IMP"); break;
                }
            }
            break;
        default: ws_die(pc, "malformed arithmetic IMP"); break;
    }
}

void
process_imp_flowcontrol(uint8_t * code, size_t * pc, int64_t ** sp, size_t * labels,
                        size_t ** rsp)
{
    switch (next_code_byte(code,pc)) {
        case '\n':
            /* Technically another LF is required but we ignore it. */
            fflush(stdout);
            unset_terminal_mode();
            exit(EXIT_SUCCESS);
        case ' ':
            {
                switch (next_code_byte(code,pc)) {
                    case ' ':
                        /* Mark a location in the program. */
                        if (next_code_byte(code,pc) != '\v') ws_die(pc,"expected vtab, "
                                "perhaps a whitespace program, rather than vvhitespace?");
                        /* Jump to next instruction since labels were parsed during startup. */
                        parse_label(code, pc);
                        break;
                    case '\t':
                        /* Call a subroutine. */
                        {
                            size_t temp_pc = labels[parse_label(code, pc)];
                            *((*rsp)++) = *pc;
                            *pc = temp_pc;
                        }
                        break;
                    case '\n':
                        /* Jump unconditionally to a label. */
                        *pc = labels[parse_label(code, pc)];
                        break;
                    default:
                        ws_die(pc, "malformed flow control IMP");
                        break;
                }
            }
            break;
        case '\t':
            {
                switch (next_code_byte(code,pc)) {
                    case ' ':
                        /* Jump to a label if TOS == 0 */
                        if (stack_pop(sp) == 0) *pc = labels[parse_label(code, pc)];
                        break;
                    case '\t':
                        /* Jump to a label if TOS < 0. */
                        if (stack_pop(sp) < 0) *pc = labels[parse_label(code, pc)];
                        break;
                    case '\n':
                        /* Return from subroutine. */
                        *pc = *(--(*rsp));
                        break;
                    default:
                        ws_die(pc, "malformed flow control IMP");
                        break;
                }
            }
            break;
        default:
            ws_die(pc, "malformed flow control IMP");
            break;
    }
}

void
process_imp_heap(uint8_t * code, size_t * pc, int64_t ** sp, int64_t ** hp)
{
    switch (next_code_byte(code,pc)) {
        case ' ' :
            /* Store to heap */
            {
                int64_t value = stack_pop(sp);
                int64_t addr  = stack_pop(sp);
                *(*hp + addr) = value;
            }
            break;
        case '\t':
            /* Retrieve from heap */
            stack_push(sp, *(*hp + stack_pop(sp)));
            break;
        default:
            ws_die(pc, "malformed heap IMP");
            break;
    }
}

void
process_imp_io(uint8_t * code, size_t * pc, int64_t ** sp, int64_t ** hp)
{
    switch (next_code_byte(code,pc)) {
        case ' ':
            /* Output */
            {
                switch (next_code_byte(code,pc)) {
                    case ' ' : /* Output char from TOS  */ printf("%c", (uint8_t) stack_pop(sp));     break;
                    case '\t': /* Output digit from TOS */ printf("%c", (uint8_t) stack_pop(sp)+'0'); break;
                    default  : ws_die(pc, "malformed output IMP");                          break;
                }
                fflush(stdout);
            }
            break;
        case '\t':
            /* Input */
            {
                while (stdin_empty()) continue;
                char c = getchar();
                switch (next_code_byte(code,pc)) {
                    case '\t': /* Input digit     */ c -= '0';                /* fallthrough */
                    case ' ' : /* Input character */ *(*hp + *(--(*sp))) = c; break;
                    default  : ws_die(pc, "malformed input IMP");             break;
                }
            }
            break;
        default: ws_die(pc, "malformed i/o IMP"); break;
    }
}

int
main(int argc, char ** argv)
{
    /*
     * Process command line arguments
     */
    int c;
    FILE * input = NULL;
    while ((c = getopt(argc,argv,"i:h")) != -1) {
        switch (c) {
            case 'i':
                if ((input = fopen(optarg, "r")) == NULL) {
                    fprintf(stderr, "ERROR: %s: %s\n", optarg, strerror(errno));
                }
                break;
            case 'h':
                print_usage(argv);
                exit(EXIT_SUCCESS);
                break;
            default:
                break;
        }
    }
    if (input == NULL) {
        fprintf(stderr, "ERROR: Must specify a VVhitespace source file with -f flag.\n");
        print_usage(argv);
        exit(EXIT_FAILURE);
    }

    /*
     * Read just the VVhitespace source code into memory, stripping comment characters.
     * We will use the array indices as addresses for the virtual PC when jumping to labels.
     */
    size_t ws_code_size = 0;
    uint8_t temp_byte;
    while (fread(&temp_byte, 1, 1, input)) {
        if (temp_byte == ' ' || temp_byte == '\t' || temp_byte == '\n' || temp_byte == '\v') {
            ws_code_size++;
        }
    }
    rewind(input);
    uint8_t * ws_code_space = malloc(ws_code_size);
    ws_code_size = 0;
    while (fread(&temp_byte, 1, 1, input)) {
        if (temp_byte == ' ' || temp_byte == '\t' || temp_byte == '\n' || temp_byte == '\v') {
            ws_code_space[ws_code_size++] = temp_byte;
        }
    }
    fclose(input);

    /*
     * Setup a stack and heap.
     */
    int64_t * hp = malloc(HEAPSIZE*sizeof(int64_t));
    int64_t * sp = malloc(DATASTACKSIZE*sizeof(int64_t));

    /* 
     * Setup the return stack and the label array.
     */
    size_t * rsp = malloc(RETURNSTACKSIZE*sizeof(size_t));
    size_t labels[65536] = {0}; /* 65536 = 2^16 => Holds all possible labels.               */
                                /* Default value of zero indicates an uninitialized label.  */
    populate_labels(labels, ws_code_space, ws_code_size);

    /*
     * Main Loop
     */
    set_terminal_mode();
    size_t pc = 0; /* Virtual program counter. Operates in the ws_code_space[] address space. */
    while (1) {
        if (pc >= ws_code_size) {
            fprintf(stderr, "SIM_ERROR: PC Overrun\n    Requested PC: %lu\n    Max Address: %lu\n",
                pc, ws_code_size-1);
            exit(EXIT_FAILURE);
            unset_terminal_mode();
        }

        /* Decode the IMPs */
        switch (ws_code_space[pc++]) {
            case ' ':
                /* Stack Manipulation */
                process_imp_stack(ws_code_space, &pc, &sp);
                break;
            case '\n':
                /* Flow Control */
                process_imp_flowcontrol(ws_code_space, &pc, &sp, labels, &rsp);
                break;
            case '\t':
                /* Arithmetic, Heap Access, or I/O */
                {
                    switch (ws_code_space[pc++]) {
                        case ' ':
                            /* Arithmetic */
                            process_imp_arithmetic(ws_code_space, &pc, &sp);
                            break;
                        case '\t':
                            /* Heap Access */
                            process_imp_heap(ws_code_space, &pc, &sp, &hp);
                            break;
                        case '\n':
                            /* I/O */
                            process_imp_io(ws_code_space, &pc, &sp, &hp);
                            break;
                    }
                }
                break;
            default: ws_die(&pc, "unexpected byte"); break;
        }
    }
}
Commit	Line	Data
1adfc4f4 AT	1	/*
	2	* (c) 2019 Aaron Taylor <ataylor at subgeniuskitty dot com>
	3	* All rights reserved.
	4	*/
	5
	6	#include <stdio.h>
	7	#include <stdlib.h>
	8	#include <unistd.h>
	9	#include <string.h>
	10	#include <errno.h>
	11	#include <stdint.h>
	12	#include <sys/select.h>
	13	#include <getopt.h>
a2664738	14	#include <termios.h>
1adfc4f4 AT	15
	16	#define VERSION 1
	17
eea0db3f AT	18	#define HEAPSIZE 1024 /* Size of heap in words */
	19	#define DATASTACKSIZE 1024 /* Size of stack in words */
	20	#define RETURNSTACKSIZE 1024 /* Max subroutine call depth */
1adfc4f4 AT	21
	22	void
	23	print_usage(char ** argv)
	24	{
bf43fa3f	25	printf( "VVhitespace Interpreter v%d (www.subgeniuskitty.com)\n"
1adfc4f4 AT	26	"Usage: %s -i <file>\n"
1adfc4f4 AT	27	" -h Help (prints this message)\n"
bf43fa3f	28	" -i <file> Specify a VVhitespace source file to interpret.\n"
1adfc4f4 AT	29	, VERSION, argv[0]
	30	);
	31	}
	32
	33	int
	34	stdin_empty(void)
	35	{
	36	fd_set read_fds;
	37	FD_ZERO(&read_fds);
	38	FD_SET(STDIN_FILENO, &read_fds);
	39
	40	struct timeval timeout;
	41	timeout.tv_sec = 0;
	42	timeout.tv_usec = 0;
	43
	44	int retval = select(1, &read_fds, NULL, NULL, &timeout);
	45	/* retval could be -1. Ignoring that for now. */
	46	if (retval > 0) return 0;
	47	return 1;
	48	}
	49
a2664738 AT	50	void
	51	set_terminal_mode(void)
	52	{
	53	struct termios options;
	54	tcgetattr(STDIN_FILENO, &options);
	55	/* Create a cbreak-like environment through the following options. */
	56	options.c_lflag &= ~ECHO; /* Disable echoing of input characters. */
	57	options.c_lflag &= ~ICANON; /* Disable cooked/line-oriented mode. */
	58	options.c_cc[VMIN] = 1;
	59	options.c_cc[VTIME] = 0;
	60	tcsetattr(STDIN_FILENO, TCSANOW, &options);
	61	}
	62
	63	void
	64	unset_terminal_mode(void)
	65	{
	66	struct termios options;
	67	tcgetattr(STDIN_FILENO, &options);
	68	/* Undo the changes made in set_terminal_mode(). */
	69	options.c_lflag \|= ECHO; /* Enable echoing of input characters. */
	70	options.c_lflag \|= ICANON; /* Enable cooked/line-oriented mode. */
	71	options.c_cc[VMIN] = 1; /* Default value from /usr/src/sys/sys/ttydefaults.h */
	72	options.c_cc[VTIME] = 0; /* Default value from /usr/src/sys/sys/ttydefaults.h */
	73	tcsetattr(STDIN_FILENO, TCSANOW, &options);
	74	}
	75
1adfc4f4 AT	76	void
	77	ws_die(size_t * pc, char * msg)
	78	{
1adfc4f4 AT	79	printf("SIM_ERROR @ PC %lu: %s\n", *pc, msg);
1adfc4f4 AT	80	fflush(stdout);
a2664738	81	unset_terminal_mode();
1adfc4f4 AT	82	exit(EXIT_FAILURE);
	83	}
	84
	85	void
eea0db3f	86	stack_push(int64_t ** sp, int64_t word)
1adfc4f4 AT	87	{
	88	((sp)++) = word;
	89	}
	90
eea0db3f AT	91	int64_t
eea0db3f AT	92	stack_pop(int64_t ** sp)
1adfc4f4 AT	93	{
	94	return (--(sp));
	95	}
	96
eea0db3f AT	97	int64_t
eea0db3f AT	98	stack_peek(int64_t ** sp, size_t offset)
1adfc4f4 AT	99	/* offset=0 peeks TOS, offset=1 peeks NOS, etc. */
	100	{
	101	return ((sp)-offset-1);
	102	}
	103
	104	uint8_t
	105	next_code_byte(uint8_t * code, size_t * pc)
	106	{
	107	return code[(*pc)++];
	108	}
	109
9686c901 AT	110	/*
	111	* In addition to returning the parsed label, this function advances the PC to
	112	* the next instruction.
	113	*/
1adfc4f4 AT	114	uint16_t
	115	parse_label(uint8_t * code, size_t * pc)
	116	{
	117	uint16_t label = 0;
	118	uint8_t c;
	119	while ((c = code[(*pc)++]) != '\n') {
	120	label = label << 1;
	121	if (c == ' ') label++;
	122	}
9686c901 AT	123	// TODO: Where should I handle attempts to access an unitialized label?
9686c901 AT	124	// For now, leave it undefined in a nasal demon sense.
1adfc4f4 AT	125	return label;
	126	}
	127
bf43fa3f	128	void
eea0db3f	129	populate_labels(size_t * labels, uint8_t * code, size_t code_size)
bf43fa3f	130	{
9686c901 AT	131	size_t cp = 0;
	132	while (cp <= code_size) {
	133	if (code[cp] == '\v') {
	134	uint16_t temp_label = parse_label(code, &cp);
	135	labels[temp_label] = cp;
	136	}
	137	cp++;
	138	}
bf43fa3f AT	139	}
bf43fa3f AT	140
1adfc4f4	141	void
eea0db3f	142	process_imp_stack(uint8_t * code, size_t * pc, int64_t ** sp)
1adfc4f4 AT	143	{
	144	switch (next_code_byte(code,pc)) {
	145	case ' ':
	146	/* Push number onto TOS. */
	147	{
	148	/* First, pick off the sign */
eea0db3f	149	int64_t sign = 0;
1adfc4f4 AT	150	switch (next_code_byte(code,pc)) {
	151	case ' ' : sign = 1; break;
	152	case '\t': sign = -1; break;
bf43fa3f	153	default : ws_die(pc, "expected sign"); break;
1adfc4f4 AT	154	}
	155
	156	/* Now, construct the number and push to TOS. */
	157	/* I'm assuming the numbers are read MSb first. */
eea0db3f AT	158	int64_t number = 0;
eea0db3f AT	159	uint8_t temp;
1adfc4f4	160	while ((temp = next_code_byte(code,pc)) != '\n') {
bf43fa3f	161	if (temp == '\v') ws_die(pc, "non-binary digit in number");
1adfc4f4 AT	162	number <<= 1;
	163	if (temp == '\t') number++;
	164	}
	165	stack_push(sp, number*sign);
	166	}
	167	break;
	168	case '\n':
	169	/* Stack sub-command */
	170	{
	171	switch (next_code_byte(code,pc)) {
	172	/* Duplicate the TOS. */
	173	case ' ':
	174	stack_push(sp, stack_peek(sp,0));
	175	break;
	176	/* Swap TOS and NOS. */
	177	case '\t':
	178	{
eea0db3f AT	179	int64_t t1 = stack_pop(sp);
eea0db3f AT	180	int64_t t2 = stack_pop(sp);
1adfc4f4 AT	181	stack_push(sp, t1);
	182	stack_push(sp, t2);
	183	}
	184	break;
	185	/* Discard TOS. */
	186	case '\n':
	187	stack_pop(sp);
	188	break;
bf43fa3f AT	189	default:
	190	ws_die(pc, "malformed stack IMP");
	191	break;
1adfc4f4 AT	192	}
	193	}
	194	break;
bf43fa3f	195	default: ws_die(pc, "malformed stack IMP"); break;
1adfc4f4 AT	196	}
	197	}
	198
	199	void
eea0db3f	200	process_imp_arithmetic(uint8_t * code, size_t * pc, int64_t ** sp)
1adfc4f4	201	{
eea0db3f	202	int64_t temp;
1adfc4f4 AT	203	switch (next_code_byte(code,pc)) {
	204	case ' ':
	205	{
	206	switch (next_code_byte(code,pc)) {
	207	case ' ':
	208	/* Addition */
	209	stack_push(sp, stack_pop(sp)+stack_pop(sp));
	210	break;
	211	case '\t':
	212	/* Subtraction */
	213	temp = stack_pop(sp);
	214	stack_push(sp, stack_pop(sp)-temp);
	215	break;
	216	case '\n':
	217	/* Multiplication */
	218	stack_push(sp, stack_pop(sp)*stack_pop(sp));
	219	break;
bf43fa3f AT	220	default:
	221	ws_die(pc, "malformed arithmetic IMP");
	222	break;
1adfc4f4 AT	223	}
	224	}
	225	break;
	226	case '\t':
	227	{
	228	switch (next_code_byte(code,pc)) {
	229	case ' ':
	230	/* Division */
	231	temp = stack_pop(sp);
	232	stack_push(sp, stack_pop(sp)/temp);
	233	break;
	234	case '\t':
	235	/* Modulo */
	236	temp = stack_pop(sp);
	237	stack_push(sp, stack_pop(sp)%temp);
	238	break;
bf43fa3f	239	default: ws_die(pc, "malformed arithmetic IMP"); break;
1adfc4f4 AT	240	}
	241	}
	242	break;
bf43fa3f	243	default: ws_die(pc, "malformed arithmetic IMP"); break;
1adfc4f4 AT	244	}
	245	}
	246
	247	void
eea0db3f AT	248	process_imp_flowcontrol(uint8_t * code, size_t * pc, int64_t ** sp, size_t * labels,
eea0db3f AT	249	size_t ** rsp)
1adfc4f4 AT	250	{
	251	switch (next_code_byte(code,pc)) {
	252	case '\n':
	253	/* Technically another LF is required but we ignore it. */
1adfc4f4	254	fflush(stdout);
a2664738	255	unset_terminal_mode();
1adfc4f4 AT	256	exit(EXIT_SUCCESS);
	257	case ' ':
	258	{
	259	switch (next_code_byte(code,pc)) {
	260	case ' ':
	261	/* Mark a location in the program. */
9686c901 AT	262	if (next_code_byte(code,pc) != '\v') ws_die(pc,"expected vtab, "
	263	"perhaps a whitespace program, rather than vvhitespace?");
	264	/* Jump to next instruction since labels were parsed during startup. */
1e574f5b	265	parse_label(code, pc);
1adfc4f4 AT	266	break;
	267	case '\t':
	268	/* Call a subroutine. */
519b6ab4 AT	269	{
	270	size_t temp_pc = labels[parse_label(code, pc)];
	271	((rsp)++) = *pc;
	272	*pc = temp_pc;
	273	}
1adfc4f4 AT	274	break;
	275	case '\n':
	276	/* Jump unconditionally to a label. */
	277	*pc = labels[parse_label(code, pc)];
	278	break;
bf43fa3f AT	279	default:
	280	ws_die(pc, "malformed flow control IMP");
	281	break;
1adfc4f4 AT	282	}
	283	}
	284	break;
	285	case '\t':
	286	{
	287	switch (next_code_byte(code,pc)) {
	288	case ' ':
	289	/* Jump to a label if TOS == 0 */
140262a9	290	if (stack_pop(sp) == 0) *pc = labels[parse_label(code, pc)];
1adfc4f4 AT	291	break;
	292	case '\t':
	293	/* Jump to a label if TOS < 0. */
140262a9	294	if (stack_pop(sp) < 0) *pc = labels[parse_label(code, pc)];
1adfc4f4 AT	295	break;
	296	case '\n':
	297	/* Return from subroutine. */
	298	pc = (--(*rsp));
	299	break;
bf43fa3f AT	300	default:
	301	ws_die(pc, "malformed flow control IMP");
	302	break;
1adfc4f4 AT	303	}
	304	}
	305	break;
bf43fa3f AT	306	default:
	307	ws_die(pc, "malformed flow control IMP");
	308	break;
1adfc4f4 AT	309	}
	310	}
	311
	312	void
eea0db3f	313	process_imp_heap(uint8_t * code, size_t * pc, int64_t sp, int64_t hp)
1adfc4f4 AT	314	{
1adfc4f4 AT	315	switch (next_code_byte(code,pc)) {
aea85838 AT	316	case ' ' :
	317	/* Store to heap */
	318	{
eea0db3f AT	319	int64_t value = stack_pop(sp);
eea0db3f AT	320	int64_t addr = stack_pop(sp);
aea85838 AT	321	(hp + addr) = value;
	322	}
	323	break;
	324	case '\t':
	325	/* Retrieve from heap */
	326	stack_push(sp, (hp + stack_pop(sp)));
	327	break;
	328	default:
	329	ws_die(pc, "malformed heap IMP");
	330	break;
1adfc4f4 AT	331	}
	332	}
	333
	334	void
eea0db3f	335	process_imp_io(uint8_t * code, size_t * pc, int64_t sp, int64_t hp)
1adfc4f4 AT	336	{
	337	switch (next_code_byte(code,pc)) {
	338	case ' ':
	339	/* Output */
	340	{
	341	switch (next_code_byte(code,pc)) {
eea0db3f AT	342	case ' ' : /* Output char from TOS */ printf("%c", (uint8_t) stack_pop(sp)); break;
eea0db3f AT	343	case '\t': /* Output digit from TOS */ printf("%c", (uint8_t) stack_pop(sp)+'0'); break;
9686c901	344	default : ws_die(pc, "malformed output IMP"); break;
1adfc4f4 AT	345	}
	346	fflush(stdout);
	347	}
	348	break;
	349	case '\t':
	350	/* Input */
	351	{
	352	while (stdin_empty()) continue;
	353	char c = getchar();
	354	switch (next_code_byte(code,pc)) {
	355	case '\t': /* Input digit / c -= '0'; / fallthrough */
a2664738	356	case ' ' : /* Input character / (hp + (--(*sp))) = c; break;
9686c901	357	default : ws_die(pc, "malformed input IMP"); break;
1adfc4f4 AT	358	}
	359	}
	360	break;
bf43fa3f	361	default: ws_die(pc, "malformed i/o IMP"); break;
1adfc4f4 AT	362	}
	363	}
	364
1adfc4f4 AT	365	int
	366	main(int argc, char ** argv)
	367	{
	368	/*
	369	* Process command line arguments
	370	*/
	371	int c;
	372	FILE * input = NULL;
	373	while ((c = getopt(argc,argv,"i:h")) != -1) {
	374	switch (c) {
	375	case 'i':
	376	if ((input = fopen(optarg, "r")) == NULL) {
	377	fprintf(stderr, "ERROR: %s: %s\n", optarg, strerror(errno));
	378	}
	379	break;
	380	case 'h':
	381	print_usage(argv);
	382	exit(EXIT_SUCCESS);
	383	break;
	384	default:
	385	break;
	386	}
	387	}
	388	if (input == NULL) {
bf43fa3f	389	fprintf(stderr, "ERROR: Must specify a VVhitespace source file with -f flag.\n");
1adfc4f4 AT	390	print_usage(argv);
	391	exit(EXIT_FAILURE);
	392	}
	393
	394	/*
eea0db3f	395	* Read just the VVhitespace source code into memory, stripping comment characters.
1adfc4f4 AT	396	* We will use the array indices as addresses for the virtual PC when jumping to labels.
	397	*/
	398	size_t ws_code_size = 0;
	399	uint8_t temp_byte;
	400	while (fread(&temp_byte, 1, 1, input)) {
bf43fa3f AT	401	if (temp_byte == ' ' \|\| temp_byte == '\t' \|\| temp_byte == '\n' \|\| temp_byte == '\v') {
	402	ws_code_size++;
	403	}
1adfc4f4 AT	404	}
	405	rewind(input);
	406	uint8_t * ws_code_space = malloc(ws_code_size);
	407	ws_code_size = 0;
	408	while (fread(&temp_byte, 1, 1, input)) {
bf43fa3f AT	409	if (temp_byte == ' ' \|\| temp_byte == '\t' \|\| temp_byte == '\n' \|\| temp_byte == '\v') {
	410	ws_code_space[ws_code_size++] = temp_byte;
	411	}
1adfc4f4 AT	412	}
	413	fclose(input);
	414
	415	/*
	416	* Setup a stack and heap.
1adfc4f4	417	*/
eea0db3f AT	418	int64_t * hp = malloc(HEAPSIZE*sizeof(int64_t));
eea0db3f AT	419	int64_t * sp = malloc(DATASTACKSIZE*sizeof(int64_t));
1adfc4f4 AT	420
	421	/*
	422	* Setup the return stack and the label array.
	423	*/
eea0db3f AT	424	size_t * rsp = malloc(RETURNSTACKSIZE*sizeof(size_t));
	425	size_t labels[65536] = {0}; /* 65536 = 2^16 => Holds all possible labels. */
	426	/* Default value of zero indicates an uninitialized label. */
bf43fa3f	427	populate_labels(labels, ws_code_space, ws_code_size);
1adfc4f4 AT	428
	429	/*
	430	* Main Loop
	431	*/
a2664738	432	set_terminal_mode();
1adfc4f4 AT	433	size_t pc = 0; /* Virtual program counter. Operates in the ws_code_space[] address space. */
	434	while (1) {
	435	if (pc >= ws_code_size) {
bf43fa3f AT	436	fprintf(stderr, "SIM_ERROR: PC Overrun\n Requested PC: %lu\n Max Address: %lu\n",
bf43fa3f AT	437	pc, ws_code_size-1);
1adfc4f4	438	exit(EXIT_FAILURE);
a2664738	439	unset_terminal_mode();
1adfc4f4 AT	440	}
	441
	442	/* Decode the IMPs */
	443	switch (ws_code_space[pc++]) {
	444	case ' ':
	445	/* Stack Manipulation */
	446	process_imp_stack(ws_code_space, &pc, &sp);
	447	break;
	448	case '\n':
	449	/* Flow Control */
	450	process_imp_flowcontrol(ws_code_space, &pc, &sp, labels, &rsp);
	451	break;
	452	case '\t':
	453	/* Arithmetic, Heap Access, or I/O */
	454	{
	455	switch (ws_code_space[pc++]) {
	456	case ' ':
	457	/* Arithmetic */
	458	process_imp_arithmetic(ws_code_space, &pc, &sp);
	459	break;
	460	case '\t':
	461	/* Heap Access */
	462	process_imp_heap(ws_code_space, &pc, &sp, &hp);
	463	break;
	464	case '\n':
	465	/* I/O */
	466	process_imp_io(ws_code_space, &pc, &sp, &hp);
	467	break;
	468	}
	469	}
	470	break;
eea0db3f	471	default: ws_die(&pc, "unexpected byte"); break;
1adfc4f4 AT	472	}
1adfc4f4 AT	473	}
1adfc4f4	474	}