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From:   "Matthew Wilcox (Oracle)" <willy@infradead.org>
To:     Andrew Morton <akpm@linux-foundation.org>
Cc:     "Matthew Wilcox (Oracle)" <willy@infradead.org>,
        linux-arch@vger.kernel.org, linux-mm@kvack.org,
        linux-kernel@vger.kernel.org
Subject: [PATCH v5 01/38] minmax: Add in_range() macro
Date:   Mon, 10 Jul 2023 21:43:02 +0100
Message-Id: <20230710204339.3554919-2-willy@infradead.org>
In-Reply-To: <20230710204339.3554919-1-willy@infradead.org>
References: <20230710204339.3554919-1-willy@infradead.org>
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Determine if a value lies within a range more efficiently (subtraction +
comparison vs two comparisons and an AND).  It also has useful (under
some circumstances) behaviour if the range exceeds the maximum value of
the type.

Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
---
 include/linux/minmax.h | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)

diff --git a/include/linux/minmax.h b/include/linux/minmax.h
index 396df1121bff..028069a1f7ef 100644
--- a/include/linux/minmax.h
+++ b/include/linux/minmax.h
@@ -158,6 +158,32 @@
  */
 #define clamp_val(val, lo, hi) clamp_t(typeof(val), val, lo, hi)
 
+static inline bool in_range64(u64 val, u64 start, u64 len)
+{
+	return (val - start) < len;
+}
+
+static inline bool in_range32(u32 val, u32 start, u32 len)
+{
+	return (val - start) < len;
+}
+
+/**
+ * in_range - Determine if a value lies within a range.
+ * @val: Value to test.
+ * @start: First value in range.
+ * @len: Number of values in range.
+ *
+ * This is more efficient than "if (start <= val && val < (start + len))".
+ * It also gives a different answer if @start + @len overflows the size of
+ * the type by a sufficient amount to encompass @val.  Decide for yourself
+ * which behaviour you want, or prove that start + len never overflow.
+ * Do not blindly replace one form with the other.
+ */
+#define in_range(val, start, len)					\
+	sizeof(start) <= sizeof(u32) ? in_range32(val, start, len) :	\
+		in_range64(val, start, len)
+
 /**
  * swap - swap values of @a and @b
  * @a: first value
-- 
2.39.2