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lib: Add strongly typed 64bit int_sqrt

PATCH Superseded Crt Mori 3 participants 5 messages Dec 19, 2017 – Dec 20, 2017

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Library code IIO

v7 of 13 Superseded Latest is v13 →

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Crt Mori

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#0 lore raw

PATCH v7 1/3 lib: Add strongly typed 64bit int_sqrt

There is no option to perform 64bit integer sqrt on 32bit platform. Added stronger typed int_sqrt64 enables the 64bit calculations to be performed on 32bit platforms. Although int_sqrt() is a rough approximation, the same algorithm is used in int_sqrt64() as good enough on 32bit platform.

Signed-off-by Crt Mori <[email protected]>
---
 include/linux/kernel.h |  6 ++++++
 lib/int_sqrt.c         | 32 ++++++++++++++++++++++++++++++++
 2 files changed, 38 insertions(+)
include/linux/kernel.h +6 -0
index 0ad4c3044cf9..f3bebd3a9213 100644
@@ -459,6 +459,12 @@ extern int kernel_text_address(unsigned long addr);
 extern int func_ptr_is_kernel_text(void *ptr);
 
 unsigned long int_sqrt(unsigned long);
+#if BITS_PER_LONG != 64
+#define int_sqrt64 _int_sqrt64
+u32 _int_sqrt64(u64 x);
+#else
+#define int_sqrt64 int_sqrt
+#endif
 
 extern void bust_spinlocks(int yes);
 extern int oops_in_progress;		/* If set, an oops, panic(), BUG() or die() is in progress */
lib/int_sqrt.c +32 -0
index 1ef4cc344977..84c77c934ec3 100644
@@ -36,3 +36,35 @@ unsigned long int_sqrt(unsigned long x)
 	return y;
 }
 EXPORT_SYMBOL(int_sqrt);
+
+#if BITS_PER_LONG != 64
+/**
+ *
+ * int_sqrt64 - strongly typed int_sqrt function when minimum 64 bit input
+ * is expected.
+ * @x: 64bit integer of which to calculate the sqrt
+ */
+u32 _int_sqrt64(u64 x)
+{
+	u64 b, m, y = 0;
+
+	if (x <= 1)
+		return x;
+
+	m = 1ULL << (64 - 2);
+	while (m != 0) {
+		b = y + m;
+		y >>= 1;
+
+		if (x >= b) {
+			x -= b;
+			y += m;
+		}
+		m >>= 2;
+	}
+
+	return y;
+}
+EXPORT_SYMBOL(_int_sqrt64);
+#endif
+
Signature · 1 line
2.15.0
#1 lore raw
Quoted 17 lines · Crt Mori

There is no option to perform 64bit integer sqrt on 32bit platform. Added stronger typed int_sqrt64 enables the 64bit calculations to be performed on 32bit platforms. Although int_sqrt() is a rough approximation, the same algorithm is used in int_sqrt64() as good enough on 32bit platform.

Signed-off-by Crt Mori <[email protected]>
---
 include/linux/kernel.h |  6 ++++++
 lib/int_sqrt.c         | 32 ++++++++++++++++++++++++++++++++
 2 files changed, 38 insertions(+)
include/linux/kernel.h +0 -0
index 0ad4c3044cf9..f3bebd3a9213 100644

include/linux/kernel.h extern int kernel_text_address(unsigned long addr); · line 467

Quoted 9 lines
include/linux/kernel.h +6 -0
@@ -459,6 +459,12 @@ extern int kernel_text_address(unsigned long addr);
 extern int func_ptr_is_kernel_text(void *ptr);
 
 unsigned long int_sqrt(unsigned long);
+#if BITS_PER_LONG != 64
+#define int_sqrt64 _int_sqrt64
+u32 _int_sqrt64(u64 x);
+#else
+#define int_sqrt64 int_sqrt
+#endif

As you've changed the return type for the 64-bit function to u32, there is a unsigned long / u32 return mismatch on 64 bit platforms.

I suspect you need to define this as:

#define int_sqrt64(x) ((u32)int_sqrt(x))

lib/int_sqrt.c

Quoted 1 line
lib/int_sqrt.c +0 -0

[]

Quoted 10 lines
lib/int_sqrt.c +6 -0
@@ -36,3 +36,35 @@ unsigned long int_sqrt(unsigned long x)
 	return y;
 }
 EXPORT_SYMBOL(int_sqrt);
+
+#if BITS_PER_LONG != 64
+/**
+ *
+ * int_sqrt64 - strongly typed int_sqrt function when minimum 64 bit input
+ * is expected.

lib/int_sqrt.c unsigned long int_sqrt(unsigned long x) · line 54

Quoted 10 lines
lib/int_sqrt.c +10 -0
+ * @x: 64bit integer of which to calculate the sqrt
+ */
+u32 _int_sqrt64(u64 x)
+{
+	u64 b, m, y = 0;
+
+	if (x <= 1)
+		return x;
+
+	m = 1ULL << (64 - 2);

Should probably use fls64 here.

Quoted 16 lines
lib/int_sqrt.c +16 -0
+	while (m != 0) {
+		b = y + m;
+		y >>= 1;
+
+		if (x >= b) {
+			x -= b;
+			y += m;
+		}
+		m >>= 2;
+	}
+
+	return y;
+}
+EXPORT_SYMBOL(_int_sqrt64);
+#endif
+
#2 lore raw
Quoted 4 lines · Joe Perches

I suspect you need to define this as:

#define int_sqrt64(x) ((u32)int_sqrt(x))

What's wrong with using C ?

static inline u32 int_sqrt64(u64 x)

{
	return int_sqrt(x);
}
#3 lore raw
Quoted 7 lines · Peter Zijlstra
Quoted 4 lines · Joe Perches

I suspect you need to define this as:

#define int_sqrt64(x) ((u32)int_sqrt(x))

What's wrong with using C ?

Duh. Nothing at all.

Quoted 4 lines

static inline u32 int_sqrt64(u64 x)

{
	return int_sqrt(x);
}
author
#4 lore raw

Thanks for suggestions and comments. Respinned v9 with them.

Quoted 15 lines · Joe Perches
Quoted 7 lines · Peter Zijlstra
Quoted 4 lines · Joe Perches

I suspect you need to define this as:

#define int_sqrt64(x) ((u32)int_sqrt(x))

What's wrong with using C ?

Duh. Nothing at all.

Quoted 4 lines

static inline u32 int_sqrt64(u64 x)

{
      return int_sqrt(x);
}