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Improve algorithm min/max #1365

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0c46944
Improve algorithm min/max
monarchdodra Jun 22, 2013
f4d51e6
min max unittest
monarchdodra Jun 22, 2013
880a22d
Make MinType and MaxType private templates.
monarchdodra Jun 23, 2013
7c91764
Documentation tweak about min max return value.
monarchdodra Jun 23, 2013
d399818
splice min/max with less/greater predicates
monarchdodra Jun 23, 2013
9048310
tweak conditions in less/greater
monarchdodra Jun 23, 2013
57eaffa
Improve less/greater more
monarchdodra Jun 23, 2013
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140 changes: 104 additions & 36 deletions std/algorithm.d
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Original file line number Diff line number Diff line change
Expand Up @@ -6159,7 +6159,7 @@ unittest
}

// MinType
template MinType(T...)
private template MinType(T...)
{
static assert(T.length >= 2);
static if (T.length == 2)
Expand All @@ -6186,32 +6186,57 @@ template MinType(T...)
}
}

//less
/*
Returns $(D true) if $(D a) is smaller than $(D b). Unlike $(D <), $(D less)
will properly handle arguments with unmatched size or sign
*/ //named algoLess while private because of @@@10375@@@
private bool algoLess(T1, T2)(T1 a, T2 b)
{
static if (isIntegral!T1 && isIntegral!T2 &&
(mostNegative!T1 < 0) != (mostNegative!T2 < 0))
{
static if (mostNegative!T1 < 0)
{
static if (T1.sizeof > T2.sizeof)
return a < b;
else static if (T2.sizeof <= 4)
{
alias T = Select!(T2.sizeof < 4, int, long);
return cast(T)a < cast(T)b;
}
else
return a < b || a < 0;
}
else //if(mostNegative!T2 < 0)
{
static if (T2.sizeof > T1.sizeof)
return a < b;
else static if (T1.sizeof <= 4)
{
alias T = Select!(T1.sizeof < 4, int, long);
return cast(T)a < cast(T)b;
}
else
return a < b && b >= 0;
}
}
else
return a < b;
}

// min
/**
Returns the minimum of the passed-in values. The type of the result is
computed by using $(XREF traits, CommonType).
Returns the minimum of the passed-in values. The result is of a type
with the correct size and sign to hold the result.
*/
MinType!(T1, T2, T) min(T1, T2, T...)(T1 a, T2 b, T xs)
if (is(typeof(a < b)))
{
static if (T.length == 0)
{
static if (isIntegral!T1 && isIntegral!T2 &&
(mostNegative!T1 < 0) != (mostNegative!T2 < 0))
{
static if (mostNegative!T1 < 0)
immutable chooseB = b < a && a > 0;
else
immutable chooseB = b < a || b < 0;
}
else
immutable chooseB = b < a;
return cast(typeof(return)) (chooseB ? b : a);
}
return cast(typeof(return)) (b.algoLess(a) ? b : a);
else
{
return min(min(a, b), xs);
}
}

unittest
Expand All @@ -6233,6 +6258,15 @@ unittest
static assert(is(typeof(min(a, f)) == int));
assert(min(a, f) == -10);

int s4 = -20_000;
ushort u2 = 33_000;
short s2 = -20_000;
uint u4 = 33_000;
assert(min(s2, u2) == s2);
assert(min(s4, u2) == s4);
assert(min(s2, u4) == s2);
assert(min(s4, u4) == s4);

//Test user-defined types
import std.datetime;
assert(min(Date(2012, 12, 21), Date(1982, 1, 4)) == Date(1982, 1, 4));
Expand All @@ -6246,7 +6280,7 @@ unittest
}

// MaxType
template MaxType(T...)
private template MaxType(T...)
{
static assert(T.length >= 2);
static if (T.length == 2)
Expand All @@ -6264,10 +6298,49 @@ template MaxType(T...)
}
}

//greater
/*
Returns $(D true) if $(D a) is greater than $(D b). Unlike $(D <), $(D greater)
will properly handle arguments with unmatched size or sign
*/ //named algoGreater while private because of @@@10375@@@
private bool algoGreater(T1, T2)(T1 a, T2 b)
{
static if (isIntegral!T1 && isIntegral!T2 &&
(mostNegative!T1 < 0) != (mostNegative!T2 < 0))
{
static if (mostNegative!T1 < 0)
{
static if (T1.sizeof > T2.sizeof)
return a > b;
else static if (T2.sizeof <= 4)
{
alias T = Select!(T2.sizeof < 4, int, long);
return cast(T)a > cast(T)b;
}
else
return a > b && a >= 0;
}
else //if(mostNegative!T2 < 0)
{
static if (T2.sizeof > T1.sizeof)
return a > b;
else static if (T1.sizeof <= 4)
{
alias T = Select!(T1.sizeof < 4, int, long);
return cast(T)a > cast(T)b;
}
else
return a > b || b < 0;
}
}
else
return a > b;
}

// max
/**
Returns the maximum of the passed-in values. The type of the result is
computed by using $(XREF traits, CommonType).
Returns the maximum of the passed-in values. The result is of a type
with the correct size and sign to hold the result.

Example:
----
Expand All @@ -6286,23 +6359,9 @@ MaxType!(T1, T2, T) max(T1, T2, T...)(T1 a, T2 b, T xs)
if (is(typeof(a < b)))
{
static if (T.length == 0)
{
static if (isIntegral!T1 && isIntegral!T2 &&
(mostNegative!T1 < 0) != (mostNegative!T2 < 0))
{
static if (mostNegative!T1 < 0)
immutable chooseB = b > a || a < 0;
else
immutable chooseB = b > a && b > 0;
}
else
immutable chooseB = b > a;
return cast(typeof(return)) (chooseB ? b : a);
}
return cast(typeof(return)) (b.algoGreater(a) ? b : a);
else
{
return max(max(a, b), xs);
}
}

unittest
Expand All @@ -6324,6 +6383,15 @@ unittest
static assert(is(typeof(max(a, f)) == uint));
assert(max(a, f) == 5);

int s4 = -20_000;
ushort u2 = 33_000;
short s2 = -20_000;
uint u4 = 33_000;
assert(max(s2, u2) == u2);
assert(max(s4, u2) == u2);
assert(max(s2, u4) == u4);
assert(max(s4, u4) == u4);

//Test user-defined types
import std.datetime;
assert(max(Date(2012, 12, 21), Date(1982, 1, 4)) == Date(2012, 12, 21));
Expand Down