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version 2.080.0

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Function std.math.cmp

Defines a total order on all floating-point numbers.

int cmp(T) (
  const(T) x,
  const(T) y
) pure nothrow @nogc @trusted
if (isFloatingPoint!T);

The order is defined as follows:

  • All numbers in [-∞, +∞] are ordered the same way as by built-in comparison, with the exception of -0.0, which is less than +0.0;
  • If the sign bit is set (that is, it's 'negative'), NAN is less than any number; if the sign bit is not set (it is 'positive'), NAN is greater than any number;
  • NANs of the same sign are ordered by the payload ('negative' ones - in reverse order).

Returns

negative value if x precedes y in the order specified above; 0 if x and y are identical, and positive value otherwise.

See Also

isIdentical

Standards

Conforms to IEEE 754-2008

Example

Most numbers are ordered naturally. 

assert(cmp(-double.infinity, -double.max) < 0);
assert(cmp(-double.max, -100.0) < 0);
assert(cmp(-100.0, -0.5) < 0);
assert(cmp(-0.5, 0.0) < 0);
assert(cmp(0.0, 0.5) < 0);
assert(cmp(0.5, 100.0) < 0);
assert(cmp(100.0, double.max) < 0);
assert(cmp(double.max, double.infinity) < 0);

writeln(cmp(1.0, 1.0)); // 0

Example

Positive and negative zeroes are distinct. 

assert(cmp(-0.0, +0.0) < 0);
assert(cmp(+0.0, -0.0) > 0);

Example

Depending on the sign, NANs go to either end of the spectrum. 

assert(cmp(-double.nan, -double.infinity) < 0);
assert(cmp(double.infinity, double.nan) < 0);
assert(cmp(-double.nan, double.nan) < 0);

Example

NANs of the same sign are ordered by the payload. 

assert(cmp(NaN(10), NaN(20)) < 0);
assert(cmp(-NaN(20), -NaN(10)) < 0);

Authors

Walter Bright, Don Clugston, Conversion of CEPHES math library to D by Iain Buclaw and David Nadlinger

License

Boost License 1.0.