RE: [PATCH 1/2] lib: int_sqrt: add int64_sqrt routine

Hello,

quoted

maybe the code could be #MACRO()'d to avoid duplication

Do you mean to define int64_sqrt() directly as int_sqrt() on a 64 bit 
platform where sizeof(long) == sizeof(long long)?

something along the lines of

#define INT_SQRT(name, type) \
   type name(type x) \ 
      type m, y = 0, b; \
...

INT_SQRT(int_sqrt, unsigned long);
INT_SQRT(int64_sqrt, unsigned long long);

not sure if it is worth it

regards, p.

________________________________________
From: Peter Meerwald [pmeerw@pmeerw.net]
Sent: Monday, June 23, 2014 5:52 PM
To: Barry Song
Cc: dmitry.torokhov@gmail.com; dtor@mail.ru; akpm@linux-foundation.org; linux-input@vger.kernel.org; DL-SHA-WorkGroupLinux; Yibo Cai; Barry Song
Subject: Re: [PATCH 1/2] lib: int_sqrt: add int64_sqrt routine

quoted

Get square root of a 64-bit digit on 32bit platforms. CSR SiRFSoC
touchscreen driver needs it.

maybe the code could be #MACRO()'d to avoid duplication

see comment below

quoted

diff --git a/include/linux/kernel.h b/include/linux/kernel.h
index 4c52907..6e63081 100644
--- a/include/linux/kernel.h
+++ b/include/linux/kernel.h

@@ -418,6 +418,7 @@ struct pid;
 extern struct pid *session_of_pgrp(struct pid *pgrp);

 unsigned long int_sqrt(unsigned long);
+unsigned long long int64_sqrt(unsigned long long);

 extern void bust_spinlocks(int yes);
 extern int oops_in_progress;         /* If set, an oops, panic(), BUG() or die() is in progress */

diff --git a/lib/int_sqrt.c b/lib/int_sqrt.c
index 1ef4cc3..2aa9fcc 100644
--- a/lib/int_sqrt.c
+++ b/lib/int_sqrt.c

@@ -36,3 +36,30 @@ unsigned long int_sqrt(unsigned long x)
      return y;
 }
 EXPORT_SYMBOL(int_sqrt);
+
+/*
+ * Square root of a 64-bit digit.
+ * Same as int_sqrt on 64-bit platforms where "long" equals "long long"
+ */
+unsigned long long int64_sqrt(unsigned long long x)
+{
+     unsigned long long m = 0, y = 0, b = 0;

initialization for b, m not needed

the original int_sqrt() code correctly skips initialization

quoted

+
+     if (x <= 1)
+             return x;
+
+     m = 1ULL << (BITS_PER_LONG_LONG - 2);
+     while (m != 0) {
+             b = y + m;
+             y >>= 1;
+
+             if (x >= b) {
+                     x -= b;
+                     y += m;
+             }
+             m >>= 2;
+     }
+
+     return y;
+}
+EXPORT_SYMBOL(int64_sqrt);

--

Peter Meerwald
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-- 

Peter Meerwald
+43-664-2444418 (mobile)