linux-kernel - [PATCH v2 09/28] vsprintf: Improve number()

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Message-Id: <20220519172421.162394-10-kent.overstreet@gmail.com>
Date:   Thu, 19 May 2022 13:24:02 -0400
From:   Kent Overstreet <kent.overstreet@...il.com>
To:     linux-kernel@...r.kernel.org, linux-mm@...r.kernel.org,
        pmladek@...e.com, rostedt@...dmis.org, senozhatsky@...omium.org
Cc:     Kent Overstreet <kent.overstreet@...il.com>,
        andriy.shevchenko@...ux.intel.com, willy@...radead.org
Subject: [PATCH v2 09/28] vsprintf: Improve number()

This patch refactors number() to make it a bit clearer, and it also
changes it to call printbuf_make_room() only once at the start, instead
of in the printbuf output helpers.

Signed-off-by: Kent Overstreet <kent.overstreet@...il.com>
---
 lib/vsprintf.c | 84 ++++++++++++++++++++++++++------------------------
 1 file changed, 43 insertions(+), 41 deletions(-)

diff --git a/lib/vsprintf.c b/lib/vsprintf.c
index 7fbeaf50d1..d1372c0b37 100644
--- a/lib/vsprintf.c
+++ b/lib/vsprintf.c
@@ -453,92 +453,94 @@ void number(struct printbuf *out, unsigned long long num,
 {
 	/* put_dec requires 2-byte alignment of the buffer. */
 	char tmp[3 * sizeof(num)] __aligned(2);
-	char sign;
-	char locase;
+	char sign = 0;
+	/* locase = 0 or 0x20. ORing digits or letters with 'locase'
+	 * produces same digits or (maybe lowercased) letters */
+	char locase = (spec.flags & SMALL);
 	int need_pfx = ((spec.flags & SPECIAL) && spec.base != 10);
-	int i;
 	bool is_zero = num == 0LL;
 	int field_width = spec.field_width;
 	int precision = spec.precision;
+	int nr_digits = 0;
+	int output_bytes = 0;
 
-	/* locase = 0 or 0x20. ORing digits or letters with 'locase'
-	 * produces same digits or (maybe lowercased) letters */
-	locase = (spec.flags & SMALL);
 	if (spec.flags & LEFT)
 		spec.flags &= ~ZEROPAD;
-	sign = 0;
 	if (spec.flags & SIGN) {
 		if ((signed long long)num < 0) {
 			sign = '-';
 			num = -(signed long long)num;
-			field_width--;
+			output_bytes++;
 		} else if (spec.flags & PLUS) {
 			sign = '+';
-			field_width--;
+			output_bytes++;
 		} else if (spec.flags & SPACE) {
 			sign = ' ';
-			field_width--;
+			output_bytes++;
 		}
 	}
 	if (need_pfx) {
 		if (spec.base == 16)
-			field_width -= 2;
+			output_bytes += 2;
 		else if (!is_zero)
-			field_width--;
+			output_bytes++;
 	}
 
 	/* generate full string in tmp[], in reverse order */
-	i = 0;
-	if (num < spec.base)
-		tmp[i++] = hex_asc_upper[num] | locase;
-	else if (spec.base != 10) { /* 8 or 16 */
+	if (spec.base == 10) {
+		nr_digits = put_dec(tmp, num) - tmp;
+	} else { /* 8 or 16 */
 		int mask = spec.base - 1;
-		int shift = 3;
+		int shift = ilog2((unsigned) spec.base);
 
-		if (spec.base == 16)
-			shift = 4;
 		do {
-			tmp[i++] = (hex_asc_upper[((unsigned char)num) & mask] | locase);
+			tmp[nr_digits++] = (hex_asc_upper[((unsigned char)num) & mask] | locase);
 			num >>= shift;
 		} while (num);
-	} else { /* base 10 */
-		i = put_dec(tmp, num) - tmp;
 	}
 
 	/* printing 100 using %2d gives "100", not "00" */
-	if (i > precision)
-		precision = i;
+	precision = max(nr_digits, precision);
+	output_bytes += precision;
+	field_width = max(0, field_width - output_bytes);
+
+	printbuf_make_room(out, field_width + output_bytes);
+
 	/* leading space padding */
-	field_width = max(0, field_width - precision);
 	if (!(spec.flags & (ZEROPAD | LEFT))) {
-		pr_chars(out, ' ', field_width);
+		__pr_chars_reserved(out, ' ', field_width);
 		field_width = 0;
 	}
+
 	/* sign */
 	if (sign)
-		__pr_char(out, sign);
+		__pr_char_reserved(out, sign);
+
 	/* "0x" / "0" prefix */
 	if (need_pfx) {
 		if (spec.base == 16 || !is_zero)
-			__pr_char(out, '0');
+			__pr_char_reserved(out, '0');
 		if (spec.base == 16)
-			__pr_char(out, 'X' | locase);
+			__pr_char_reserved(out, 'X' | locase);
 	}
-	/* zero or space padding */
-	if (!(spec.flags & LEFT)) {
-		char c = ' ' + (spec.flags & ZEROPAD);
 
-		pr_chars(out, c, field_width);
-		field_width = 0;
-	}
-	/* hmm even more zero padding? */
-	if (precision > i)
-		pr_chars(out, '0', precision - i);
+	/* zero padding */
+	if (!(spec.flags & LEFT))
+		__pr_chars_reserved(out, '0', field_width);
+
+	/* zero padding from precision */
+	if (precision > nr_digits)
+		__pr_chars_reserved(out, '0', precision - nr_digits);
+
 	/* actual digits of result */
-	while (--i >= 0)
-		__pr_char(out, tmp[i]);
+	while (--nr_digits >= 0)
+		__pr_char_reserved(out, tmp[nr_digits]);
+
 	/* trailing space padding */
-	pr_chars(out, ' ', field_width);
+	if (spec.flags & LEFT)
+		__pr_chars_reserved(out, ' ', field_width);
+
+	printbuf_nul_terminate(out);
 }
 
 static noinline_for_stack
-- 
2.36.0