linux-kernel - [PATCH nolibc 25/61] tools/nolibc/stdlib: avoid a 64-bit shift in u64toh

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Message-Id: <20220419004225.3952530-25-paulmck@kernel.org>
Date:   Mon, 18 Apr 2022 17:41:49 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     linux-kernel@...r.kernel.org
Cc:     gwml@...r.gnuweeb.org, kernel-team@...com, w@....eu,
        Willy Tarreau <w@....eu>,
        "Paul E . McKenney" <paulmck@...nel.org>
Subject: [PATCH nolibc 25/61] tools/nolibc/stdlib: avoid a 64-bit shift in u64toh_r()

From: Willy Tarreau <w@....eu>

The build of printf() on mips requires libgcc for functions __ashldi3 and
__lshrdi3 due to 64-bit shifts when scanning the input number. These are
not really needed in fact since we scan the number 4 bits at a time. Let's
arrange the loop to perform two 32-bit shifts instead on 32-bit platforms.

Signed-off-by: Willy Tarreau <w@....eu>
Signed-off-by: Paul E. McKenney <paulmck@...nel.org>
---
 tools/include/nolibc/stdlib.h | 16 ++++++++++------
 1 file changed, 10 insertions(+), 6 deletions(-)

diff --git a/tools/include/nolibc/stdlib.h b/tools/include/nolibc/stdlib.h
index 82a4cf606d3c..db47362a750f 100644
--- a/tools/include/nolibc/stdlib.h
+++ b/tools/include/nolibc/stdlib.h
@@ -200,14 +200,18 @@ int u64toh_r(uint64_t in, char *buffer)
 	int dig;
 
 	do {
-		dig = in >> pos;
-		in -= (uint64_t)dig << pos;
+		if (sizeof(long) >= 8) {
+			dig = (in >> pos) & 0xF;
+		} else {
+			/* 32-bit platforms: avoid a 64-bit shift */
+			uint32_t d = (pos >= 32) ? (in >> 32) : in;
+			dig = (d >> (pos & 31)) & 0xF;
+		}
+		if (dig > 9)
+			dig += 'a' - '0' - 10;
 		pos -= 4;
-		if (dig || digits || pos < 0) {
-			if (dig > 9)
-				dig += 'a' - '0' - 10;
+		if (dig || digits || pos < 0)
 			buffer[digits++] = '0' + dig;
-		}
 	} while (pos >= 0);
 
 	buffer[digits] = 0;
-- 
2.31.1.189.g2e36527f23