digitalmars.D.bugs - [Issue 2973] New: std.math.pow(int, int), etc.
- d-bugmail puremagic.com (19/19) May 13 2009 http://d.puremagic.com/issues/show_bug.cgi?id=2973
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http://d.puremagic.com/issues/show_bug.cgi?id=2973
Summary: std.math.pow(int, int), etc.
Product: D
Version: 2.030
Platform: PC
OS/Version: Windows
Status: NEW
Severity: enhancement
Priority: P2
Component: Phobos
AssignedTo: bugzilla digitalmars.com
ReportedBy: dsimcha yahoo.com
std.math should have a function for efficiently and accurately computing
int^int, int ^ uint, etc. Casting to floating point is not a good solution b/c
you lose performance and, in some cases, precision. Furthermore, this would be
dead simple to implement.
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May 13 2009
d-bugmail puremagic.com
http://d.puremagic.com/issues/show_bug.cgi?id=2973
ZHOU Zhenyu <rinick gmail.com> changed:
What |Removed |Added
----------------------------------------------------------------------------
CC| |rinick gmail.com
std.math should have a function for efficiently and accurately computing
int^int, int ^ uint, etc. Casting to floating point is not a good solution b/c
you lose performance and, in some cases, precision. Furthermore, this would be
dead simple to implement.
agree
int^uint and long^uint are useful.
but int^int is not necessary, because:
int a = pow(2,-1); this doesn't make any sense.
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Jul 21 2009
http://d.puremagic.com/issues/show_bug.cgi?id=2973
Andrei Alexandrescu <andrei metalanguage.com> changed:
What |Removed |Added
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CC| |andrei metalanguage.com
19:19:38 PDT ---
We currently have:
pure nothrow F pow(F)(F x, uint n) if (isFloatingPoint!(F));
pure nothrow F pow(F)(F x, int n) if (isFloatingPoint!(F));
F pow(F)(F x, F y) if (isFloatingPoint!(F));
I think we're in good shape. We could add overloads for raising integrals to
unsigned powers but I fear confusion due to wraparound. The magnitudes of
exponents for which efficiency could become an issue are also those that would
wraparound the result. If no compelling arguments come up, I'll close this
soon.
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Jul 21 2009
http://d.puremagic.com/issues/show_bug.cgi?id=2973 --- Couldn't you just stick an assert in there to make sure it doesn't wrap around? I haven't tested, but I would think that even in debug mode, this would be faster than using the float version. -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
Jul 21 2009
http://d.puremagic.com/issues/show_bug.cgi?id=2973 20:15:20 PDT ---Couldn't you just stick an assert in there to make sure it doesn't wrap around? I haven't tested, but I would think that even in debug mode, this would be faster than using the float version.1. Please test. What powers are you looking at? For most bases and most exponents the result will go off range. 2. I prefer returning a floating point number instead of attempting to return an integer and failing dynamically, all for a doubtful speed benefit. -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
Jul 21 2009
http://d.puremagic.com/issues/show_bug.cgi?id=2973What powers are you looking at? For most bases and most exponents the result will go off range.long a = foo(); long b = a * a * a; I don't want to call foo() again. So I have to define one more variable just because pow doesn't accept integer. (In fact, I have a longPow function and I use it from time to time) -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
Jul 21 2009
http://d.puremagic.com/issues/show_bug.cgi?id=2973
Don <clugdbug yahoo.com.au> changed:
What |Removed |Added
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CC| |clugdbug yahoo.com.au
Casting to floating point is not a good solution b/c
you lose performance and, in some cases, precision.
Are you sure?
Performance:
Floating point multiplication is typically the same speed or faster than
integer multiplication on most CPUs from the past 15 years. On most Intel CPUs,
integer multiplication is actually done in the floating point unit.
Precision:
You'll only lose precision if the base is greater than the 1/real.epsilon. For
an 80-bit real, this means precision is lost only when the result is exactly
equal to ulong.max. And the only time that can happen is with pow(ulong.max,
1).
(because ulong.max is divisible by 5, but not by 25).
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Aug 11 2009
http://d.puremagic.com/issues/show_bug.cgi?id=2973
Andrei Alexandrescu <andrei metalanguage.com> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|NEW |ASSIGNED
AssignedTo|nobody puremagic.com |andrei metalanguage.com
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Oct 11 2009
http://d.puremagic.com/issues/show_bug.cgi?id=2973
David Simcha <dsimcha yahoo.com> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|ASSIGNED |RESOLVED
Resolution| |WONTFIX
Since I filed this one and I'm thoroughly convinced now that it's not necessary
and noone else seems to want it, I'm resolving it as WONTFIX.
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Oct 18 2009
http://d.puremagic.com/issues/show_bug.cgi?id=2973 13:06:15 PDT ---Since I filed this one and I'm thoroughly convinced now that it's not necessary and noone else seems to want it, I'm resolving it as WONTFIX.Thanks for following through. -- Configure issuemail: http://d.puremagic.com/issues/userprefs.cgi?tab=email ------- You are receiving this mail because: -------
Oct 18 2009
http://d.puremagic.com/issues/show_bug.cgi?id=2973
ZY Zhou <rinick gmail.com> changed:
What |Removed |Added
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Status|RESOLVED |REOPENED
Resolution|WONTFIX |
Now we have power operator.
It will be very confusing that 3.0^^3 works but 3^^3 doesn't. Most people would
think ^^ in D is just like ** in python.
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Dec 04 2009
http://d.puremagic.com/issues/show_bug.cgi?id=2973
Don <clugdbug yahoo.com.au> changed:
What |Removed |Added
----------------------------------------------------------------------------
Status|REOPENED |RESOLVED
Resolution| |FIXED
FIXED: 3^^3 works in DMD 2.040.
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Feb 12 2010