arch/x86_64/core/printf.h

/*
 * Copyright (c) 2018 Intel Corporation
 *
 * SPDX-License-Identifier: Apache-2.0
 */
#include <stdarg.h>

/* Tiny, but not-as-primitive-as-it-looks implementation of something
 * like s/n/printf().  Handles %d, %x, %c and %s only, no precision
 * specifiers or type modifiers.
 */

struct _pfr {
	char *buf;
	int len;
	int idx;
};

/* Set this function pointer to something that generates output */
static void (*z_putchar)(int c);

static void pc(struct _pfr *r, int c)
{
	if (r->buf) {
		if (r->idx <= r->len)
			r->buf[r->idx] = c;
	} else {
		z_putchar(c);
	}
	r->idx++;
}

static void prdec(struct _pfr *r, int v)
{
	if (v < 0) {
		pc(r, '-');
		v = -v;
	}

	char digs[11];
	int i = 10;

	digs[i--] = 0;
	while (v || i == 9) {
		digs[i--] = '0' + (v % 10);
		v /= 10;
	}

	while (digs[++i])
		pc(r, digs[i]);
}

static void endrec(struct _pfr *r)
{
	if (r->buf && r->idx < r->len)
		r->buf[r->idx] = 0;
}

static int vpf(struct _pfr *r, const char *f, va_list ap)
{
	for (/**/; *f; f++) {
		if (*f != '%') {
			pc(r, *f);
			continue;
		}

		switch (*(++f)) {
		case '%':
			pc(r, '%');
			break;
		case 'c':
			pc(r, va_arg(ap, int));
			break;
		case 's': {
			char *s = va_arg(ap, char *);

			while (*s)
				pc(r, *s++);
			break;
		}
		case 'p':
			pc(r, '0');
			pc(r, 'x'); /* fall through... */
		case 'x': {
			int sig = 0;
			unsigned int v = va_arg(ap, unsigned int);

			for (int i = 7; i >= 0; i--) {
				int d = (v >> (i*4)) & 0xf;

				sig += !!d;
				if (sig || i == 0)
					pc(r, "0123456789abcdef"[d]);
			}
			break;
		}
		case 'd':
			prdec(r, va_arg(ap, int));
			break;
		default:
			pc(r, '%');
			pc(r, *f);
		}
	}
	endrec(r);
	return r->idx;
}

#define CALL_VPF(rec)				\
	va_list ap;				\
	va_start(ap, f);			\
	int ret = vpf(&r, f, ap);		\
	va_end(ap);				\
	return ret

static inline int snprintf(char *buf, unsigned long len, const char *f, ...)
{
	struct _pfr r = { .buf = buf, .len = len };

	CALL_VPF(&r);
}

static inline int sprintf(char *buf, const char *f, ...)
{
	struct _pfr r = { .buf = buf, .len = 0x7fffffff };

	CALL_VPF(&r);
}

static inline int printf(const char *f, ...)
{
	struct _pfr r = {0};

	CALL_VPF(&r);
}