strbuf: add strbuf_add_uint()

strbuf_addf() calls vsnprintf(3) underneath, which supports a plethora
of formatting options.  We can avoid its overhead in basic cases by
providing specialized functions like strbuf_addstr() for strings.  Add
another one, strbuf_add_uint(), for unsigned integers.

Prepare the number string in a temporary buffer.  Make it big enough for
any unsigned integer value: A decimal digit can represent ln(10)/ln(2) ≈
3.32 bits; dividing the number of bits of uintmax_t by 3.3 and rounding
up gives a sufficiently close conservative size estimate.

Signed-off-by: René Scharfe <l.s.r@web.de>
Signed-off-by: Junio C Hamano <gitster@pobox.com>

strbuf.c

@@ -361,6 +361,18 @@ void strbuf_addf(struct strbuf *sb, const char *fmt, ...)
 	va_end(ap);
 }
 
+void strbuf_add_uint(struct strbuf *sb, uintmax_t value)
+{
+	char buf[DIV_ROUND_UP(bitsizeof(value) * 10, 33)];
+	char *end = buf + sizeof(buf);
+	char *p = end;
+
+	do
+		*--p = "0123456789"[value % 10];
+	while (value /= 10);
+	strbuf_add(sb, p, end - p);
+}
+
 static void add_lines(struct strbuf *out,
 			const char *prefix,
 			const char *buf, size_t size,

strbuf.h

@@ -410,6 +410,12 @@ void strbuf_humanise_rate(struct strbuf *buf, off_t bytes);
 __attribute__((format (printf,2,3)))
 void strbuf_addf(struct strbuf *sb, const char *fmt, ...);
 
+
+/**
+ * Add an unsigned decimal number.
+ */
+void strbuf_add_uint(struct strbuf *sb, uintmax_t value);
+
 /**
  * Add a formatted string prepended by a comment character and a
  * blank to the buffer.