Introduce `tf_snprintf`

This is a reduced version of `snprintf` that only supports formats '%d',
'%i' and '%u'. It can be used when the full `snprintf` is not needed in
order to save memory. If it finds an unknown format specifier, it
prints an error message and panics.

Change-Id: I2cb06fcdf74cda2c43caf73ae0762a91499fc04e
Signed-off-by: Antonio Nino Diaz <antonio.ninodiaz@arm.com>

Makefile

@@ -150,6 +150,7 @@ include lib/stdlib/stdlib.mk
 
 BL_COMMON_SOURCES	+=	common/bl_common.c			\
 				common/tf_printf.c			\
+				common/tf_snprintf.c			\
 				common/${ARCH}/debug.S			\
 				lib/${ARCH}/cache_helpers.S		\
 				lib/${ARCH}/misc_helpers.S		\

common/tf_snprintf.c

@@ -0,0 +1,108 @@
+/*
+ * Copyright (c) 2017, ARM Limited and Contributors. All rights reserved.
+ *
+ * SPDX-License-Identifier: BSD-3-Clause
+ */
+
+#include <debug.h>
+#include <platform.h>
+#include <stdarg.h>
+
+static void unsigned_dec_print(char **s, size_t n, size_t *chars_printed,
+			       unsigned int unum)
+{
+	/* Enough for a 32-bit unsigned decimal integer (4294967295). */
+	unsigned char num_buf[10];
+	int i = 0, rem;
+
+	do {
+		rem = unum % 10;
+		num_buf[i++] = '0' + rem;
+	} while (unum /= 10);
+
+	while (--i >= 0) {
+		if (*chars_printed < n)
+			*(*s)++ = num_buf[i];
+		(*chars_printed)++;
+	}
+}
+
+/*******************************************************************
+ * Reduced snprintf to be used for Trusted firmware.
+ * The following type specifiers are supported:
+ *
+ * %d or %i - signed decimal format
+ * %u - unsigned decimal format
+ *
+ * The function panics on all other formats specifiers.
+ *
+ * It returns the number of characters that would be written if the
+ * buffer was big enough. If it returns a value lower than n, the
+ * whole string has been written.
+ *******************************************************************/
+int tf_snprintf(char *s, size_t n, const char *fmt, ...)
+{
+	va_list args;
+	int num;
+	unsigned int unum;
+	size_t chars_printed = 0;
+
+	if (n == 1) {
+		/* Buffer is too small to actually write anything else. */
+		*s = '\0';
+		n = 0;
+	} else if (n >= 2) {
+		/* Reserve space for the terminator character. */
+		n--;
+	}
+
+	va_start(args, fmt);
+	while (*fmt) {
+
+		if (*fmt == '%') {
+			fmt++;
+			/* Check the format specifier. */
+			switch (*fmt) {
+			case 'i':
+			case 'd':
+				num = va_arg(args, int);
+
+				if (num < 0) {
+					if (chars_printed < n)
+						*s++ = '-';
+					chars_printed++;
+
+					unum = (unsigned int)-num;
+				} else {
+					unum = (unsigned int)num;
+				}
+
+				unsigned_dec_print(&s, n, &chars_printed, unum);
+				break;
+			case 'u':
+				unum = va_arg(args, unsigned int);
+				unsigned_dec_print(&s, n, &chars_printed, unum);
+				break;
+			default:
+				/* Panic on any other format specifier. */
+				ERROR("tf_snprintf: specifier with ASCII code '%d' not supported.",
+				      *fmt);
+				plat_panic_handler();
+			}
+			fmt++;
+			continue;
+		}
+
+		if (chars_printed < n)
+			*s++ = *fmt;
+		fmt++;
+		chars_printed++;
+	}
+
+	va_end(args);
+
+	if (n > 0)
+		*s = '\0';
+
+	return chars_printed;
+}

include/common/debug.h

@@ -64,6 +64,7 @@ void __dead2 do_panic(void);
 void __dead2 __stack_chk_fail(void);
 
 void tf_printf(const char *fmt, ...) __printflike(1, 2);
+int tf_snprintf(char *s, size_t n, const char *fmt, ...) __printflike(3, 4);
 
 #endif /* __ASSEMBLY__ */
 #endif /* __DEBUG_H__ */