kprintf: implement "full" format sequence support

So this was painful.  kprintf() supports most of
the format specifiers from BSD now, except for the
$ sequence.  It has gotten a general overhaul and
is significantly more sophisticated, bloated and
slower now.  There is also some minor stuff i
forgot about, like the 't' length modifier, but
that isn't so important right now and will be
fixed later(TM).

arch/x86/boot/boot.c

@@ -55,9 +55,9 @@ enum vga_color fb_foreground;
 #define cell_at(line, col) ( &framebuffer[(line) * FB_COLS + (col)] )
 #define current_cell (cell_at(fb_line, fb_col))
 
-static ssize_t fb_write(struct kprintf_renderer *renderer, const void *buf, size_t size);
+static ssize_t fb_write(struct kprintf_printer *renderer, const void *buf, size_t size);
-static ssize_t fb_flush(struct kprintf_renderer *renderer);
+static ssize_t fb_flush(struct kprintf_printer *renderer);
-static struct kprintf_renderer fb_kprintf_renderer = {
+static struct kprintf_printer fb_kprintf_renderer = {
 	.write = fb_write,
 	.flush = fb_flush,
 };
@@ -76,7 +76,7 @@ extern int main(int argc, char *argv[]);
 
 __asmlink void _boot(u32 magic, void *address) /* NOLINT */
 {
-	kprintf_set_renderer(&fb_kprintf_renderer);
+	kprintf_set_printer(&fb_kprintf_renderer);
 	fb_init(VGA_COLOR_LIGHT_GREY, VGA_COLOR_BLACK);
 
 	x86_setup_interrupts();
@@ -173,7 +173,7 @@ static void fb_newline(void)
 	}
 }
 
-static ssize_t fb_write(struct kprintf_renderer *renderer, const void *buf, size_t size)
+static ssize_t fb_write(struct kprintf_printer *renderer, const void *buf, size_t size)
 {
 	ssize_t ret = 0;
 	const u8 *s = buf;
@@ -200,7 +200,7 @@ static ssize_t fb_write(struct kprintf_renderer *renderer, const void *buf, size
 	return ret;
 }
 
-static ssize_t fb_flush(struct kprintf_renderer *renderer)
+static ssize_t fb_flush(struct kprintf_printer *renderer)
 {
 	return 0;
 }

arch/x86/mm/page.c

@@ -83,7 +83,7 @@ int mem_init(uintptr_t start_phys, uintptr_t end_phys)
 
 	setup_pagemap();
 
-	kprintf("Available memory: %u bytes (%u pages)\n",
+	kprintf("Available memory: %zu bytes (%lu pages)\n",
 		dynpage_end - dynpage_start, (dynpage_end - dynpage_start) / PAGE_SIZE);
 
 	return 0;

include/gay/cdefs.h

@@ -14,7 +14,9 @@
 
 #define __aligned(bytes) __attribute__(( aligned(bytes) ))
 
+#ifndef __always_inline
 #define __always_inline inline __attribute__(( always_inline ))
+#endif
 
 #define __packed __attribute__(( packed ))
 

include/gay/kprintf.h

@@ -32,41 +32,43 @@ int kprintf(const char *__restrict fmt, ...);
 int kvprintf(const char *__restrict fmt, va_list args);
 
 /**
- * @brief Renderer functions that `kprintf()` and friends call for writing.
+ * @brief Printing functions that `kprintf()` and friends call for writing.
  * Depending on the current kernel log output target (which in turn depends
- * primarily on the current boot stage), this will be implemented by different
+ * primarily on the current runlevel), this will be implemented by different
- * subsystems.  To change the renderer, call `kprintf_set_renderer()`.
+ * subsystems.  To change the printer, call `kprintf_set_printer()`.
  */
-struct kprintf_renderer {
+struct kprintf_printer {
 	/**
 	 * @brief Write to the kernel log.
+	 * The data itself may be cached in a buffer rather than written to the
+	 * target immediately; `krpintf()` will call `flush()` when needed.
 	 *
-	 * @param renderer A reference to the original structure
+	 * @param printer A reference to the original structure
 	 * @param buf Data to write
-	 * @param len Amount of data in bytes
+	 * @param len Length of `buf` in bytes
 	 * @returns The amount of bytes actually written,
 	 *	or a negative code from `errno.h` on failure
 	 */
-	ssize_t (*write)(struct kprintf_renderer *renderer, const void *buf, size_t len);
+	ssize_t (*write)(struct kprintf_printer *printer, const void *buf, size_t len);
 	/**
 	 * @brief Flush the kernel log buffer.
 	 * On implementations that don't have a buffer, this can be a no-op.
 	 * If that is the case, this call should always return 0.
 	 *
-	 * @param renderer A reference to the original structure
+	 * @param printer A reference to the original structure
 	 * @returns The amount of bytes flushed out (0 if none),
 	 *	or a negative code from `errno.h` on failure
 	 */
-	ssize_t (*flush)(struct kprintf_renderer *renderer);
+	ssize_t (*flush)(struct kprintf_printer *printer);
 };
 
 /**
- * @brief Set the current renderer for the `fprintf()` family of functions.
+ * @brief Set the current printer for the `kprintf()` family of functions.
  *
- * @param renderer Implementation of the write and flush functions
+ * @param new Implementation of the write and flush functions
  * @returns 0 on success, or a negative code from `errno.h` on failure
  */
-int kprintf_set_renderer(struct kprintf_renderer *renderer);
+int kprintf_set_printer(struct kprintf_printer *new);
 
 /*
  * This file is part of GayBSD.

include/gay/types.h

@@ -34,6 +34,11 @@ typedef __SIZE_TYPE__		ssize_t;
 typedef ssize_t			isize;
 typedef size_t			usize;
 
+typedef __INTMAX_TYPE__		intmax_t;
+typedef __UINTMAX_TYPE__	uintmax_t;
+typedef __WCHAR_TYPE__		wchar_t;
+typedef __WINT_TYPE__		wint_t;
+
 /*
  * This file is part of GayBSD.
  * Copyright (c) 2021 fef <owo@fef.moe>.

kernel/kprintf.c

@@ -1,156 +1,95 @@
 /* See the end of this file for copyright and license terms. */
 
-#include <stdarg.h> /* from clang */
+/*
+ * Ok, i'm gonna be honest, this is one of those functions where i wish i was
+ * writing them in Rust rather than C.  Anyway, the tricky part of this entire
+ * implementation is that we can't call kmalloc() because that uses kprintf()
+ * internally for debug messages and the such, so it could potentially end in an
+ * infinite loop.  But, since format strings allow arbitrary padding, we need to
+ * resort to our good old friend alloca().
+ * Also, this code is probably buggy as shit and i only tested some basic format
+ * sequences, so don't push it too far.  Be gentle.
+ * I hope i never have to touch this again.
+ */
+
+#include <alloca.h> /* clang */
+#include <stdarg.h> /* clang */
+
 #include <string.h>
 
 #include <gay/cdefs.h>
-#include <gay/config.h>
-#include <gay/errno.h>
 #include <gay/kprintf.h>
 #include <gay/types.h>
 
-#if __SIZEOF_INT__ == 2
+static struct kprintf_printer *printer = NULL;
-	/* 5 decimal digits of 65535 (2 ** 16 - 1) */
-#	define PRINTF_UINT_BUFSZ 5
-#elif __SIZEOF_INT__ == 4
-	/* 10 decimal digits of 4294967295 (2 ** 32 - 1) */
-#	define PRINTF_UINT_BUFSZ 10
-#elif __SIZEOF_INT__ == 8
-	/* 20 decimal digits of 18446744073709551616 (2 ** 64 - 1) */
-#	define PRINTF_UINT_BUFSZ 20
-#else
-#	error "Unsupported int size"
-#endif
 
-static struct kprintf_renderer *renderer = NULL;
+int kprintf_set_printer(struct kprintf_printer *new)
-
-int kprintf_set_renderer(struct kprintf_renderer *new)
 {
 	int ret = 0;
 
-	if (renderer != NULL)
+	if (printer != NULL)
-		ret = renderer->flush(renderer);
+		ret = printer->flush(printer);
 
-	renderer = new;
+	printer = new;
 	return ret;
 }
 
-static int fmt_handle_ptr(uintptr_t ptr)
+enum length_modifier {
+	LENGTH_DEFAULT = 0,
+	LENGTH_H,
+	LENGTH_HH,
+	LENGTH_L,
+	LENGTH_LL,
+	LENGTH_J,
+	LENGTH_T,
+	LENGTH_Z,
+};
+
+struct fmt_sequence {
+	isize (*render)(const struct fmt_sequence *sequence, va_list *ap);
+	unsigned int min_width;
+	unsigned int max_precision;
+	enum length_modifier length_modifier;
+	struct {
+		bool hash;
+		bool zero;
+		bool minus;
+		bool space;
+		bool plus;
+		bool apos;
+	} flags __packed; /* save some bytes on the stack :) */
+	bool uppercase;
+};
+
+static void parse_fmt_sequence(struct fmt_sequence *sequence, const char **restrict pos);
+
+/** @brief Write a NUL terminated string using the current `printer`. */
+static isize write_asciz(const char *s);
+/** @brief Write a specific amount of bytes using the current `printer`. */
+static isize write_bytes(const void *buf, usize len);
+
+int kvprintf(const char *fmt, va_list _args)
 {
-	static const char table[] = {
+	isize ret = 0;
-		'0', '1', '2', '3', '4', '5', '6', '7',
-		'8', '9', 'a', 'b', 'c', 'd', 'e', 'f',
-	};
-
-	int ret;
-	/* 2 chars per byte, plus 2 for the "0x" hex prefix */
-	char str[2 * sizeof(uintptr_t) + 2];
-	char *pos = &str[2 * sizeof(uintptr_t) + 1];
-
-	str[0] = '0';
-	str[1] = 'x';
-
-	do {
-		*pos-- = table[ptr & 0xf];
-		ptr >>= 4;
-	} while (pos != &str[1]);
-
-	ret = renderer->write(renderer, str, 2 * sizeof(uintptr_t) + 2);
-	return ret;
-}
-
-static int fmt_handle_uint(unsigned int u)
-{
-	char str[PRINTF_UINT_BUFSZ];
-	char *pos = &str[PRINTF_UINT_BUFSZ - 1];
-
-	do {
-		/* stupid big endian humans, forcing us to do the whole thing in reverse */
-		*pos-- = (char)(u % 10) + '0'; /* convert to ASCII */
-		u /= 10;
-	} while (u != 0);
-	pos++;
-
-	return (int)renderer->write(renderer, pos, PRINTF_UINT_BUFSZ - (pos - str));
-}
-
-static inline int fmt_handle_int(int i)
-{
-	int ret = 0;
-	char minus = '-';
-
-	if (i < 0) {
-		ret = renderer->write(renderer, &minus, sizeof(minus));
-		i = -i;
-	}
-
-	if (ret >= 0) {
-		int uint_ret = fmt_handle_uint((unsigned int)i);
-		if (uint_ret < 0)
-			ret = uint_ret;
-		else if (ret < 0)
-			ret += uint_ret;
-	}
-
-	return ret;
-}
-
-int kvprintf(const char *fmt, va_list args)
-{
-	ssize_t ret = 0;
 	const char *tmp = fmt;
-	union {
+	va_list args;
-		char c;
+	va_copy(args, _args);
-		int d;
-		uintptr_t p;
-		char *s;
-		unsigned int u;
-	} val;
 
 	while (*tmp != '\0') {
 		if (*tmp++ == '%') {
-			/* flush out everything we have so far (minus one char for %) */
+			/* write out everything we have so far (minus one char for %) */
-			ssize_t write_ret = renderer->write(
+			isize write_ret = write_bytes(fmt, (usize)tmp - (usize)fmt - 1);
-				renderer,
-				fmt,
-				(size_t)tmp - (size_t)fmt - 1
-			);
 			if (write_ret < 0) {
 				ret = write_ret;
 				break;
 			}
 			ret += write_ret;
 
-			ssize_t fmt_ret = 0;
+			isize fmt_ret = 0;
-			switch (*tmp) {
+			struct fmt_sequence sequence;
-			case '%': /* literal percent sign */
+			parse_fmt_sequence(&sequence, &tmp);
-				fmt_ret = renderer->write(renderer, tmp, sizeof(*tmp));
+			if (sequence.render != NULL)
-				break;
+				fmt_ret = sequence.render(&sequence, &args);
-
-			case 'c': /* char */
-				val.c = va_arg(args, int); /* POSIX wants an int */
-				fmt_ret = renderer->write(renderer, &val.c, sizeof(val.c));
-				break;
-
-			case 'd': /* int */
-			case 'i':
-				fmt_ret = fmt_handle_int(va_arg(args, int));
-				break;
-
-			case 'p': /* ptr */
-				fmt_ret = fmt_handle_ptr(va_arg(args, uintptr_t));
-				break;
-
-			case 's': /* string */
-				val.s = va_arg(args, char *);
-				fmt_ret = renderer->write(renderer, val.s, strlen(val.s));
-				break;
-
-			case 'u': /* unsigned int */
-				fmt_ret = fmt_handle_uint(va_arg(args, unsigned int));
-				break;
-			}
-			tmp++;
 
 			/*
 			 * act as if the current position were the beginning in
@@ -165,19 +104,20 @@ int kvprintf(const char *fmt, va_list args)
 	}
 
 	if (tmp != fmt && ret >= 0) {
-		ssize_t render_ret = renderer->write(renderer, fmt, (size_t)tmp - (size_t)fmt);
+		isize render_ret = write_bytes(fmt, (usize)tmp - (usize)fmt);
 		if (render_ret < 0)
 			ret = render_ret;
 		else
 			ret += render_ret;
 	}
 
-	ssize_t flush_ret = renderer->flush(renderer);
+	isize flush_ret = printer->flush(printer);
 	if (flush_ret < 0)
 		ret = flush_ret;
 	else
 		ret += flush_ret;
 
+	va_end(args);
 	return (int)ret;
 }
 
@@ -193,6 +133,447 @@ int kprintf(const char *fmt, ...)
 	return ret;
 }
 
+static isize render_c(const struct fmt_sequence *sequence, va_list *ap);
+static isize render_d(const struct fmt_sequence *sequence, va_list *ap);
+static isize render_o(const struct fmt_sequence *sequence, va_list *ap);
+static isize render_p(const struct fmt_sequence *sequence, va_list *ap);
+static isize render_s(const struct fmt_sequence *sequence, va_list *ap);
+static isize render_u(const struct fmt_sequence *sequence, va_list *ap);
+static isize render_x(const struct fmt_sequence *sequence, va_list *ap);
+static isize render_percent(const struct fmt_sequence *sequence, va_list *ap);
+
+/*
+ * Oh boi this is gonna be fun.
+ * So, this is basically a step by step implementation of the FreeBSD manpage
+ * for printf(), except that there is no support for all the deprecated
+ * specifiers and the (imho insane) $ directive:
+ * <https://www.freebsd.org/cgi/man.cgi?query=printf&sektion=3&manpath=FreeBSD+13.0-RELEASE>
+ */
+void parse_fmt_sequence(struct fmt_sequence *sequence, const char **restrict pos)
+{
+	memset(sequence, 0, sizeof(*sequence));
+
+	if (**pos == '%') { /* %% */
+		sequence->render = render_percent;
+		return;
+	}
+
+	/*
+	 * parse optional flags
+	 */
+	bool continue_parse_flags = true;
+	while (continue_parse_flags) {
+		switch (**pos) {
+		case '#':
+			sequence->flags.hash = true;
+			break;
+		case '0':
+			sequence->flags.zero = true;
+			break;
+		case '-':
+			sequence->flags.minus = true;
+			break;
+		case ' ':
+			/* the FreeBSD manpage says plus overrides space if both are used */
+			if (!sequence->flags.plus)
+				sequence->flags.space = true;
+			break;
+		case '+':
+			sequence->flags.plus = true;
+			sequence->flags.space = false;
+			break;
+		case '\'':
+			sequence->flags.apos = true;
+			break;
+		default:
+			continue_parse_flags = false;
+			break;
+		}
+		(*pos)++;
+	}
+	(*pos)--;
+
+	/*
+	 * parse optional minimum digits
+	 */
+	while (**pos >= '0' && **pos <= '9') {
+		sequence->min_width *= 10;
+		sequence->min_width += **pos - '0';
+		if (sequence->max_precision > 128)
+			sequence->max_precision = 128;
+		(*pos)++;
+	}
+
+	/*
+	 * parse optional maximum precision
+	 */
+	if (**pos == '.') {
+		(*pos)++;
+		while (**pos >= '0' && **pos <= '9') {
+			sequence->max_precision *= 10;
+			sequence->max_precision += **pos - '0';
+			/* sanitize length (prevents stack overflow) */
+			if (sequence->max_precision > 128)
+				sequence->max_precision = 128;
+			(*pos)++;
+		}
+		(*pos)--;
+	}
+
+	/*
+	 * parse optional length modifier
+	 */
+	switch (**pos) {
+	case 'h':
+	case 'H':
+		if ((*pos)[1] == 'h' || (*pos)[1] == 'H') {
+			sequence->length_modifier = LENGTH_HH;
+			(*pos) += 2;
+		} else {
+			sequence->length_modifier = LENGTH_H;
+			(*pos) += 1;
+		}
+		break;
+	case 'l':
+	case 'L':
+		if ((*pos)[1] == 'l' || (*pos)[1] == 'L') {
+			sequence->length_modifier = LENGTH_LL;
+			(*pos) += 2;
+		} else {
+			sequence->length_modifier = LENGTH_L;
+			(*pos) += 1;
+		}
+		break;
+	case 'j':
+	case 'J':
+		sequence->length_modifier = LENGTH_J;
+		(*pos)++;
+		break;
+	case 't':
+	case 'T':
+		sequence->length_modifier = LENGTH_T;
+		(*pos)++;
+		break;
+	case 'z':
+	case 'Z':
+		sequence->length_modifier = LENGTH_Z;
+		(*pos)++;
+		break;
+	default:
+		break;
+	}
+
+	/*
+	 * parse type specifier
+	 */
+	switch (**pos) {
+	case 'C':
+		sequence->length_modifier = LENGTH_L;
+		/* fall through */
+	case 'c':
+		sequence->render = render_c;
+		break;
+	case 'd':
+	case 'i':
+		sequence->render = render_d;
+		break;
+	case 'o':
+		sequence->render = render_o;
+		break;
+	case 'P':
+		sequence->uppercase = true;
+		/* fall through */
+	case 'p':
+		sequence->render = render_p;
+		break;
+	case 'S':
+		sequence->length_modifier = LENGTH_L;
+		/* fall through */
+	case 's':
+		sequence->render = render_s;
+		break;
+	case 'u':
+		sequence->render = render_u;
+		break;
+	case 'X':
+		sequence->uppercase = true;
+		/* fall through */
+	case 'x':
+		sequence->render = render_x;
+		break;
+	default:
+		sequence->render = NULL;
+		break;
+	}
+	(*pos)++;
+}
+
+static ssize_t render_c(const struct fmt_sequence *sequence, va_list *ap)
+{
+	ssize_t ret;
+
+	if (sequence->length_modifier == LENGTH_L) {
+		wchar_t val = (wchar_t)va_arg(*ap, wint_t);
+		ret = printer->write(printer, &val, sizeof(val));
+	} else {
+		char val = (char)va_arg(*ap, int);
+		ret = printer->write(printer, &val, sizeof(val));
+	}
+
+	return ret;
+}
+
+static ssize_t render_s(const struct fmt_sequence *sequence, va_list *ap)
+{
+	/* yes i know i forgot the wchar_t if the length_modifier is LENGTH_L but idgaf */
+	const char *s = va_arg(*ap, char *);
+	return write_asciz(s);
+}
+
+static inline void get_arg_signed(intmax_t *dest,
+				  const struct fmt_sequence *sequence,
+				  va_list *ap)
+{
+	switch (sequence->length_modifier) {
+	case LENGTH_H:
+	case LENGTH_HH:
+	case LENGTH_DEFAULT:
+		/* short and char will be promoted to int with parameter passing */
+		*dest = va_arg(*ap, int);
+		break;
+	case LENGTH_L:
+		*dest = va_arg(*ap, long);
+		break;
+	case LENGTH_LL:
+		*dest = va_arg(*ap, long long);
+		break;
+	case LENGTH_Z:
+		*dest = va_arg(*ap, isize);
+		break;
+	case LENGTH_J:
+		*dest = va_arg(*ap, intmax_t);
+		break;
+	case LENGTH_T:
+		*dest = va_arg(*ap, intptr_t);
+		break;
+	}
+}
+
+static inline void get_arg_unsigned(uintmax_t *dest,
+				    const struct fmt_sequence *sequence,
+				    va_list *ap)
+{
+	switch (sequence->length_modifier) {
+	case LENGTH_H:
+	case LENGTH_HH:
+	case LENGTH_DEFAULT:
+		/* short and char will be promoted to int with parameter passing */
+		*dest = va_arg(*ap, unsigned int);
+		break;
+	case LENGTH_L:
+		*dest = va_arg(*ap, unsigned long);
+		break;
+	case LENGTH_LL:
+		*dest = va_arg(*ap, unsigned long long);
+		break;
+	case LENGTH_Z:
+		*dest = va_arg(*ap, usize);
+		break;
+	case LENGTH_J:
+		*dest = va_arg(*ap, uintmax_t);
+		break;
+	case LENGTH_T:
+		*dest = va_arg(*ap, uintptr_t);
+		break;
+	}
+}
+
+static const char *digit_table_smol = "0123456789abcdef";
+static const char *digit_table_big = "0123456789ABCDEF";
+
+static inline void stringify_uint(char **buf, uintmax_t val, const char *digit_table,
+				  unsigned int radix, int direction)
+{
+	do {
+		**buf = digit_table[val % radix];
+		*buf += direction;
+	} while ((val /= radix) != 0);
+	*buf -= direction;
+}
+
+static isize render_d(const struct fmt_sequence *sequence, va_list *ap)
+{
+	isize ret = 0;
+	intmax_t val;
+	get_arg_signed(&val, sequence, ap);
+
+	if (val < 0) {
+		val = -val;
+		ret = write_asciz("-");
+		if (ret < 0)
+			return ret;
+	} else if (sequence->flags.plus) {
+		ret = write_asciz("+");
+		if (ret < 0)
+			return ret;
+	} else if (sequence->flags.space) {
+		ret = write_asciz(" ");
+		if (ret < 0)
+			return ret;
+	}
+
+	usize len = 20; /* 2**64 has 20 decimal digits, let's hope intmax_t isn't 128 bits */
+	if (sequence->min_width > len)
+		len = sequence->min_width;
+	char *buf = alloca(len);
+	char *pos = &buf[len - 1];
+
+	stringify_uint(&pos, val, digit_table_smol, 10, -1);
+	while (sequence->min_width > len - (pos - buf))
+		*--pos = '0';
+
+	isize tmp = write_bytes(pos, len - (pos - buf));
+	if (tmp > 0)
+		ret += tmp;
+	else
+		ret = tmp;
+	return ret;
+}
+
+static isize render_o(const struct fmt_sequence *sequence, va_list *ap)
+{
+	isize ret = 0;
+
+	if (sequence->flags.plus) {
+		ret = write_asciz("+");
+		if (ret < 0)
+			return ret;
+	} else if (sequence->flags.space) {
+		ret = write_asciz(" ");
+		if (ret < 0)
+			return ret;
+	}
+
+	uintmax_t val;
+	get_arg_unsigned(&val, sequence, ap);
+
+	usize len = 22; /* 2**64 has 22 octal digits, let's hope intmax_t isn't 128 bits */
+	if (sequence->min_width > len)
+		len = sequence->min_width;
+	char *buf = alloca(len);
+	char *pos = &buf[len - 1];
+
+	stringify_uint(&pos, val, digit_table_smol, 8, -1);
+	while (sequence->min_width > len - (pos - buf))
+		*--pos = '0';
+
+	isize tmp = write_bytes(pos, len - (pos - buf));
+	if (tmp > 0)
+		ret += tmp;
+	else
+		ret = tmp;
+	return ret;
+}
+
+static isize render_p(const struct fmt_sequence *sequence, va_list *ap)
+{
+	/* 2 hex digits per byte + 2 for 0x prefix */
+	char buf[sizeof(uintptr_t) * 2 + 2];
+	char *pos = &buf[sizeof(uintptr_t) * 2 + 1];
+	const char *digit_table;
+	uintptr_t ptr = va_arg(*ap, uintptr_t);
+
+	buf[0] = '0';
+	buf[1] = 'x';
+
+	if (sequence->uppercase)
+		digit_table = digit_table_big;
+	else
+		digit_table = digit_table_smol;
+
+	while (pos > &buf[1]) {
+		*pos-- = digit_table[ptr % 0x10];
+		ptr >>= 4;
+	}
+
+	return write_bytes(buf, sizeof(buf));
+}
+
+static isize render_u(const struct fmt_sequence *sequence, va_list *ap)
+{
+	isize ret = 0;
+
+	if (sequence->flags.plus) {
+		ret = write_asciz("+");
+		if (ret < 0)
+			return ret;
+	} else if (sequence->flags.space) {
+		ret = write_asciz(" ");
+		if (ret < 0)
+			return ret;
+	}
+
+	uintmax_t val;
+	get_arg_unsigned(&val, sequence, ap);
+
+	usize len = 20; /* 2^64 has 20 decimal digits, let's hope intmax_t isn't 128 bits */
+	if (sequence->min_width > len)
+		len = sequence->min_width;
+	char *buf = alloca(len);
+	char *pos = &buf[len - 1];
+
+	stringify_uint(&pos, val, digit_table_smol, 10, -1);
+	while (sequence->min_width > len - (pos - buf))
+		*--pos = '0';
+
+	isize tmp = write_bytes(pos, len - (pos - buf));
+	if (tmp > 0)
+		ret += tmp;
+	else
+		ret = tmp;
+	return ret;
+}
+
+static isize render_x(const struct fmt_sequence *sequence, va_list *ap)
+{
+	char *buf;
+	usize len = sizeof(uintmax_t) * 2; /* 2 hex digits per byte */
+	if (len < sequence->min_width)
+		len = sequence->min_width;
+	buf = alloca(len);
+	char *pos = &buf[len];
+
+	uintmax_t val;
+	get_arg_unsigned(&val, sequence, ap);
+
+	const char *digit_table;
+	if (sequence->uppercase)
+		digit_table = digit_table_big;
+	else
+		digit_table = digit_table_smol;
+
+	stringify_uint(&pos, val, digit_table, 16, -1);
+	while (sequence->min_width > len - (pos - buf))
+		*--pos = '0';
+
+	return write_bytes(pos, len - (pos - buf));
+}
+
+static isize render_percent(const struct fmt_sequence *sequence, va_list *ap)
+{
+	return write_asciz("%");
+}
+
+static inline isize write_asciz(const char *s)
+{
+	return printer->write(printer, s, strlen(s));
+}
+
+static inline isize write_bytes(const void *buf, usize len)
+{
+	return printer->write(printer, buf, len);
+}
+
 /*
  * This file is part of GayBSD.
  * Copyright (c) 2021 fef <owo@fef.moe>.