| Message ID | 20171218150544.8000-1-cmo@melexis.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
On Mon, 2017-12-18 at 16:05 +0100, Crt Mori wrote: > 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. [] > diff --git a/include/linux/kernel.h b/include/linux/kernel.h [] > @@ -459,6 +459,7 @@ extern int kernel_text_address(unsigned long addr); > extern int func_ptr_is_kernel_text(void *ptr); > > unsigned long int_sqrt(unsigned long); > +u64 int_sqrt64(u64 x); > > 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 [] > @@ -36,3 +36,29 @@ unsigned long int_sqrt(unsigned long x) > return y; > } > EXPORT_SYMBOL(int_sqrt); > + > +/** > + * int_sqrt64 - strongly typed int_sqrt function > + * @x: 64bit integer of which to calculate the sqrt > + */ > +u64 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); int_sqrt is now optimized with __fls Because u64 is unsigned long on 64 bit arches, this could probably be optimized for 64 bit distributions with something like: #if BITS_PER_LONG != 64 #define int_sqrt64 _int_sqrt64 u64 _int_sqrt64(u64 x); #else #define int_sqrt64(x) int_sqrt #endif ... #if BITS_PER_LONG != 64 u64 _int_sqrt64(u64 x) { etc.. } #endif -- To unsubscribe from this list: send the line "unsubscribe linux-iio" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Mon, Dec 18, 2017 at 04:05:44PM +0100, Crt Mori wrote: > 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. You clearly haven't read a recent version of the file you're patching. Please take a moment to do so now. > +/** > + * int_sqrt64 - strongly typed int_sqrt function > + * @x: 64bit integer of which to calculate the sqrt > + */ > +u64 int_sqrt64(u64 x) Please explain how the result of sqrt(u64) can be larger than u32. Also, I expect that this fact could be exploited to optimize this for 32bit archs if one were so inclined. > +{ > + 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; > +} so yeah, no, please try again after reading the current file. -- To unsubscribe from this list: send the line "unsubscribe linux-iio" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On 18 December 2017 at 17:44, Peter Zijlstra <peterz@infradead.org> wrote: > On Mon, Dec 18, 2017 at 04:05:44PM +0100, Crt Mori wrote: >> 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. > > You clearly haven't read a recent version of the file you're patching. > Please take a moment to do so now. > IIO kernel does not have the recent version in, so thanks for heads up. It does not change much for my function. >> +/** >> + * int_sqrt64 - strongly typed int_sqrt function >> + * @x: 64bit integer of which to calculate the sqrt >> + */ >> +u64 int_sqrt64(u64 x) > > Please explain how the result of sqrt(u64) can be larger than u32. > My hand calculator tells me it could be. ffffffff×ffffffff = FFFFFFFE00000001 which still has some margin which will end up above the 32 bit number. Further more the __fls optimization automatically casts the inputs to unsigned long (32 bit on 32 bit machines), so that also makes it out of option. > Also, I expect that this fact could be exploited to optimize this for > 32bit archs if one were so inclined. > >> +{ >> + 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; >> +} > > so yeah, no, please try again after reading the current file. -- To unsubscribe from this list: send the line "unsubscribe linux-iio" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On 18 December 2017 at 17:24, Joe Perches <joe@perches.com> wrote: > On Mon, 2017-12-18 at 16:05 +0100, Crt Mori wrote: >> 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. > [] >> diff --git a/include/linux/kernel.h b/include/linux/kernel.h > [] >> @@ -459,6 +459,7 @@ extern int kernel_text_address(unsigned long addr); >> extern int func_ptr_is_kernel_text(void *ptr); >> >> unsigned long int_sqrt(unsigned long); >> +u64 int_sqrt64(u64 x); >> >> 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 > [] >> @@ -36,3 +36,29 @@ unsigned long int_sqrt(unsigned long x) >> return y; >> } >> EXPORT_SYMBOL(int_sqrt); >> + >> +/** >> + * int_sqrt64 - strongly typed int_sqrt function >> + * @x: 64bit integer of which to calculate the sqrt >> + */ >> +u64 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); > > int_sqrt is now optimized with __fls > > Because u64 is unsigned long on 64 bit arches, this > could probably be optimized for 64 bit distributions > with something like: > > #if BITS_PER_LONG != 64 > #define int_sqrt64 _int_sqrt64 > u64 _int_sqrt64(u64 x); > #else > #define int_sqrt64(x) int_sqrt > #endif > > ... > > #if BITS_PER_LONG != 64 > u64 _int_sqrt64(u64 x) > { etc.. } > #endif > Thanks for the tip. I will respin with this change so that 64 bit arches use the optimized int_sqrt from above. -- To unsubscribe from this list: send the line "unsubscribe linux-iio" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On Tue, Dec 19, 2017 at 10:31:18AM +0100, Crt Mori wrote: > IIO kernel does not have the recent version in, so thanks for heads IIO? > up. It does not change much for my function. The comment says: * Computes: floor(sqrt(x)) floor(sqrt(2^64-1)) == 2^32-1 -- To unsubscribe from this list: send the line "unsubscribe linux-iio" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
On 19 December 2017 at 14:25, Peter Zijlstra <peterz@infradead.org> wrote: > On Tue, Dec 19, 2017 at 10:31:18AM +0100, Crt Mori wrote: >> IIO kernel does not have the recent version in, so thanks for heads > > IIO? > Industrial Input / Output Subsytem tree >> up. It does not change much for my function. > > The comment says: > > * Computes: floor(sqrt(x)) > > floor(sqrt(2^64-1)) == 2^32-1 > OK, so return value should be u32. -- To unsubscribe from this list: send the line "unsubscribe linux-iio" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html
diff --git a/include/linux/kernel.h b/include/linux/kernel.h index 0ad4c3044cf9..09f53063f2c9 100644 --- a/include/linux/kernel.h +++ b/include/linux/kernel.h @@ -459,6 +459,7 @@ extern int kernel_text_address(unsigned long addr); extern int func_ptr_is_kernel_text(void *ptr); unsigned long int_sqrt(unsigned long); +u64 int_sqrt64(u64 x); 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 1ef4cc344977..de5836448ea3 100644 --- a/lib/int_sqrt.c +++ b/lib/int_sqrt.c @@ -36,3 +36,29 @@ unsigned long int_sqrt(unsigned long x) return y; } EXPORT_SYMBOL(int_sqrt); + +/** + * int_sqrt64 - strongly typed int_sqrt function + * @x: 64bit integer of which to calculate the sqrt + */ +u64 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);
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 <cmo@melexis.com> --- include/linux/kernel.h | 1 + lib/int_sqrt.c | 26 ++++++++++++++++++++++++++ 2 files changed, 27 insertions(+)