From: Bart Van Assche <bvanassche@acm.org>
Date: Sun, 26 Aug 2018 15:54:19 +0000 (-0700)
Subject: Micro-optimize num2str()
X-Git-Tag: fio-3.10~4^2~1
X-Git-Url: https://git.kernel.dk/?p=fio.git;a=commitdiff_plain;h=3b6879b271835dabefbe7bc626cb24ecb96547c1

Micro-optimize num2str()

Instead of selecting an element from the thousand[] array several times,
perform the choice between 1000 and 1024 once. This patch does not change
any functionality.

Signed-off-by: Bart Van Assche <bvanassche@acm.org>
---

diff --git a/lib/num2str.c b/lib/num2str.c
index 40fb3aec..ff8a365b 100644
--- a/lib/num2str.c
+++ b/lib/num2str.c
@@ -30,7 +30,7 @@ char *num2str(uint64_t num, int maxlen, int base, int pow2, enum n2s_unit units)
 		[N2S_BYTEPERSEC]= "B/s",
 		[N2S_BITPERSEC]	= "bit/s"
 	};
-	const unsigned int thousand[] = { 1000, 1024 };
+	const unsigned int thousand = pow2 ? 1024 : 1000;
 	unsigned int modulo;
 	int post_index, carry = 0;
 	char tmp[32], fmt[32];
@@ -49,7 +49,7 @@ char *num2str(uint64_t num, int maxlen, int base, int pow2, enum n2s_unit units)
 		unitprefix = sistr;
 
 	for (post_index = 0; base > 1; post_index++)
-		base /= thousand[!!pow2];
+		base /= thousand;
 
 	switch (units) {
 	case N2S_NONE:
@@ -77,9 +77,9 @@ char *num2str(uint64_t num, int maxlen, int base, int pow2, enum n2s_unit units)
 		if (strlen(tmp) <= maxlen)
 			break;
 
-		modulo = num % thousand[!!pow2];
-		num /= thousand[!!pow2];
-		carry = modulo >= thousand[!!pow2] / 2;
+		modulo = num % thousand;
+		num /= thousand;
+		carry = modulo >= thousand / 2;
 		post_index++;
 	}
 
@@ -110,9 +110,9 @@ done:
 	 * Fill in everything and return the result.
 	 */
 	assert(maxlen - strlen(tmp) - 1 > 0);
-	assert(modulo < thousand[!!pow2]);
+	assert(modulo < thousand);
 	sprintf(fmt, "%%.%df", (int)(maxlen - strlen(tmp) - 1));
-	sprintf(tmp, fmt, (double)modulo / (double)thousand[!!pow2]);
+	sprintf(tmp, fmt, (double)modulo / (double)thousand);
 
 	sprintf(buf, "%llu.%s%s%s", (unsigned long long) num, &tmp[2],
 			unitprefix[post_index], unitstr[units]);