novaos/libc/stdio/printf.c

#include <limits.h>
#include <stdbool.h>
#include <stdarg.h>
#include <stdio.h>
#include <string.h>
#include <stdint.h>

#include <kernel/_kernel.h>

static void reverse(char* buf, int len)
{
	int start = 0;
	int end = len - 1;
	while (start < end) {
		char tmp = buf[start];
		buf[start] = buf[end];
		buf[end] = tmp;
		end--;
		start++;
	}
}

static char* s64toa(int64_t num, char* buf, int base)
{
	int i = 0;
	bool neg = false;
	
	if (num == 0) { // Handle zero explicitly
		buf[i++] = '0';
		buf[i] = '\0';
		return buf;
	}

	if (num < 0 && base == 10) { // only handle negative on base10
		neg = true;
		num = -num;
	}

	while (num != 0) {
		int rem = num % base;
		buf[i++] = (rem > 9) ? (rem - 10) + 'a' : rem + '0';
		num = num / base;
	}

	if (neg) // lets reapply the negative sign
		buf[i++] = '-'; 

	buf[i] = '\0';

	reverse(buf, i); // reverse, since we did it backwards!
	return buf;
}

static char* u64toa(uint64_t num, char* buf, int base)
{
	int i = 0;
	if (num == 0) { // Handle zero explicitly
		buf[i++] = '0';
		buf[i] = '\0';
		return buf;
	}

	while (num != 0) {
		int rem = num % base;
		buf[i++] = (rem > 9) ? (rem - 10) + 'a' : rem + '0';
		num = num / base;
	}

	buf[i] = '\0';

	reverse(buf, i); // reverse, since we did it backwards!
	return buf;
}

static char* itoa(int num, char* buf, int base)
{
	int i = 0;
	bool neg = false;
	
	if (num == 0) { // Handle zero explicitly
		buf[i++] = '0';
		buf[i] = '\0';
		return buf;
	}

	if (num < 0 && base == 10) { // only handle negative on base10
		neg = true;
		num = -num;
	}

	while (num != 0) {
		int rem = num % base;
		buf[i++] = (rem > 9) ? (rem - 10) + 'a' : rem + '0';
		num = num / base;
	}

	if (neg) // lets reapply the negative sign
		buf[i++] = '-'; 

	buf[i] = '\0';

	reverse(buf, i); // reverse, since we did it backwards!
	return buf;
}

static bool print(const char* data, size_t length) {
	const unsigned char* bytes = (const unsigned char*) data;
	for (size_t i = 0; i < length; i++)
		if (putchar(bytes[i]) == EOF) return false;
	return true;
}

int printf(const char* restrict format, ...) {
	va_list parameters;
	va_start(parameters, format);

	int written = 0;

	char buffer[512];

	while (*format != '\0') {
		size_t maxrem = INT_MAX - written;

		if (format[0] != '%' || format[1] == '%') {
			if (format[0] == '%')
				format++;
			size_t amount = 1;
			while (format[amount] && format[amount] != '%')
				amount++;
			if (maxrem < amount) {
				// TODO: Set errno to EOVERFLOW.
				return -1;
			}
			if (!print(format, amount))
				return -1;
			format += amount;
			written += amount;
			continue;
		}

		const char* format_begun_at = format++;

		if (*format == 'c') {
			format++;
			char c = (char) va_arg(parameters, int /* char promotes to int */);
			if (!maxrem) {
				// TODO: Set errno to EOVERFLOW.
				return -1;
			}
			if (!print(&c, sizeof(c)))
				return -1;
			written++;
		} else if (*format == 's') {
			format++;
			const char* str = va_arg(parameters, const char*);
			size_t len = strlen(str);
			if (maxrem < len) {
				// TODO: Set errno to EOVERFLOW.
				return -1;
			}
			if (!print(str, len))
				return -1;
			written += len;
		} else if (*format == 'd') {
			format++;
			int i = (int) va_arg(parameters, int);
			itoa(i, buffer, 10);
			size_t len = strlen(buffer);
			if (maxrem < len) {
				// TODO: Set errno to EOVERFLOW.
				return -1;
			}
			if (!print(buffer, len))
				return -1;
			written += len;
		} else if (*format == 'x') {
			format++;
			int i = (int) va_arg(parameters, int);
			itoa(i, buffer, 16);
			size_t len = strlen(buffer);
			if (maxrem < len) {
				// TODO: Set errno to EOVERFLOW.
				return -1;
			}
			if (!print(buffer, len))
				return -1;
			written += len;
		} else if (*format == '1') {
			format++;
			uint64_t i = (uint64_t) va_arg(parameters, uint64_t);
			u64toa(i, buffer, 10);
			size_t len = strlen(buffer);
			if (maxrem < len) {
				// TODO: Set errno to EOVERFLOW.
				return -1;
			}
			if (!print(buffer, len))
				return -1;
			written += len;
		} else if (*format == '2') {
			format++;
			uint64_t i = (uint64_t) va_arg(parameters, uint64_t);
			u64toa(i, buffer, 16);
			size_t len = strlen(buffer);
			if (maxrem < len) {
				// TODO: Set errno to EOVERFLOW.
				return -1;
			}
			if (!print(buffer, len))
				return -1;
			written += len;
		} else if (*format == '3') {
			format++;
			int64_t i = (int64_t) va_arg(parameters, int64_t);
			s64toa(i, buffer, 10);
			size_t len = strlen(buffer);
			if (maxrem < len) {
				// TODO: Set errno to EOVERFLOW.
				return -1;
			}
			if (!print(buffer, len))
				return -1;
			written += len;
		} else if (*format == '4') {
			format++;
			int64_t i = (int64_t) va_arg(parameters, int64_t);
			s64toa(i, buffer, 16);
			size_t len = strlen(buffer);
			if (maxrem < len) {
				// TODO: Set errno to EOVERFLOW.
				return -1;
			}
			if (!print(buffer, len))
				return -1;
			written += len;
		} else {
			format = format_begun_at;
			size_t len = strlen(format);
			if (maxrem < len) {
				// TODO: Set errno to EOVERFLOW.
				return -1;
			}
			if (!print(format, len))
				return -1;
			written += len;
			format += len;
		}
	}

	va_end(parameters);
	return written;
}