operating-system/src/lib/printf.c

#include <stdarg.h>
#include <limits.h>
#include <stdint.h>

#include "libc.h"
#include "kernel/tty.h"

typedef int (*printf_function)(struct printf_state* s, void* data);

constexpr int EOF = -1;

struct printf_state {
    struct str str;
    va_list ap;
    size_t i;
    int written;
};

static inline int ps_peek(struct printf_state* s)
{
    if (s->i == s->str.len) {
        return EOF;
    }
    return s->str.data[s->i];
}

static inline int ps_get(struct printf_state* s)
{
    if (s->i == s->str.len) {
        return EOF;
    }
    return s->str.data[s->i++];
}

static int print_long(unsigned long n, struct str alphabet, bool is_signed, unsigned int padding, char pad_char)
{
    constexpr size_t BUF_SZ = 128;
    char buf[BUF_SZ];
    size_t i = 0;

    if (padding > BUF_SZ) {
        return -1;
    }

    if (n == 0) {
        terminal_putchar('0');
        return 1;
    }

    bool is_negative = false;
    if (is_signed) {
        signed long signed_n = (signed long)n;
        if (signed_n < 0) {
            is_negative = true;
            n = -signed_n;
        }
    }

    if (is_negative)
        terminal_putchar('-');

    while (n) {
        i += 1;
        buf[BUF_SZ-i] = alphabet.data[n % alphabet.len];
        n /= alphabet.len;
    }
    while (i < padding) {
        i += 1;
        buf[BUF_SZ-i] = pad_char;
    }

    terminal_write((struct str){.data = &buf[BUF_SZ-i], .len = i});

    return i;
}   

static int print_i32(struct printf_state* s, int padding, char pad_char)
{
    padding  = padding ? padding : 0;
    pad_char = pad_char ? pad_char : ' ';
    uint32_t n = va_arg(s->ap, int32_t);
    return print_long(n, str_attach("0123456789"), true, padding, pad_char);
}

static int print_u32(struct printf_state* s, int padding, char pad_char)
{
    padding  = padding ? padding : 0;
    pad_char = pad_char ? pad_char : ' ';
    uint32_t n = va_arg(s->ap, uint32_t);
    return print_long(n, str_attach("0123456789"), false, padding, pad_char);
}

static int print_x32(struct printf_state* s, int padding, char pad_char)
{
    padding = padding ? padding : 0;
    pad_char = pad_char ? pad_char : '0';
    uint32_t n = va_arg(s->ap, uint32_t);
    struct str alphabet = str_attach("0123456789abcdef");
    return print_long(n, alphabet, false, padding, pad_char);
}

static int print_b32(struct printf_state* s, int padding, char pad_char)
{
    padding = padding ? padding : 32;
    pad_char = pad_char ? pad_char : '0';
    uint32_t n = va_arg(s->ap, uint32_t);
    struct str alphabet = str_attach("01");
    return print_long(n, alphabet, false, padding, pad_char);
}

static int print_str(struct printf_state* s, int padding, char pad_char)
{
    // TODO: implement padding
    (void)padding;
    (void)pad_char;
    const struct str str = va_arg(s->ap, struct str);
    for (size_t i=0; i < str.len; i++) {
        terminal_putchar(str.data[i]);
    }
    return str.len;
}

static int print_char(struct printf_state* s)
{
    // char is promoted to int when passed through va_arg
    const int ch = va_arg(s->ap, int);

    if (ch >= 32 && ch < 127) {
        terminal_putchar(ch);
        return 1;
    } else {
        return print_long(ch, str_attach("0123456789abcdef"), false, 0, 0);
    }
}

static int print_cs(struct printf_state* s)
{
    int n;
    int sum = 0;

    const uint8_t cs = va_arg(s->ap, uint32_t);

    const struct str cs_bit_names[] = {
        [0] = str_attach("ACCESSED"),
        [1] = str_attach("RW"),
        [2] = str_attach("DC"),
        [3] = str_attach("EXEC"),
        [4] = str_attach("DESCRIPTOR"),
        [7] = str_attach("PRESENT"),
    };
        
    for (size_t i = 0; i < sizeof cs_bit_names / sizeof *cs_bit_names; i++) {
        if (cs & (1<<i) && cs_bit_names[i].data) {
            n = printf(str_attach("{str} | "), cs_bit_names[i]);
            if (n == -1) {
                return -1;
            }
            sum += n;
        }
    }

    unsigned int ring = (cs>>5) & 0b11;
    n = printf(str_attach("DPL({uint})"), ring);
    if (n == -1) {
        return -1;
    }
    sum += n;

    return sum;
}

static int parse_format_cmd(struct printf_state* s)
{
    int c;
    uint32_t cmd = 0;
    int pad = 0;
    char pad_char = '\0';

    constexpr uint32_t CHAR_MASK = (1<<CHAR_BIT)-1;

    while (c = ps_get(s), c != EOF && c != '}') {
        cmd <<= CHAR_BIT;
        cmd |= c & CHAR_MASK;
    }

    if (c == EOF)
        return -1;

#pragma GCC diagnostic push
#pragma GCC diagnostic ignored "-Wmultichar"
    switch (cmd) {
        // 16 bit types are promoted to 32 bit by va_arg(...) anyways
        case 'int':
        case 'i16':
        case 'i32':
            return print_i32(s, pad, pad_char);

        case 'uint':
        case 'u16':
        case 'u32':
            return print_u32(s, pad, pad_char);

        case 'hex':
        case 'x16':
        case 'x32':
            return print_x32(s, pad, pad_char);

        case 'str':
            return print_str(s, pad, pad_char);

        case 'char':
            return print_char(s);

        case 'cs':
            return print_cs(s);

        default:
            return -1;
    }
#pragma GCC diagnostic pop
}

int printf(struct str format, ...)
{
    int c;

    struct printf_state s = {
        .str = format,
        .i = 0,
        .written = 0,
    };
    va_start(s.ap, format);

    while ((c = ps_get(&s)) != EOF) {
        switch (c) {

        case '{':
            int ok = parse_format_cmd(&s);
            if (ok == -1)
                return -1;
            s.written += ok;
            break;

        default:
            terminal_putchar(c);
            s.written += 1;
            break;
        }
    }

    return s.written;
}