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Last update Wed Sep 5 11:42:44 2007

# std.math

const real E;
  e
const real LOG2T;
  log210
const real LOG2E;
  log2e
const real LOG2;
  log102
const real LOG10E;
  log10e
const real LN2;
  ln 2
const real LN10;
  ln 10
const real PI;
  π
const real PI_2;
  π / 2
const real PI_4;
  π / 4
const real M_1_PI;
  1 / π
const real M_2_PI;
  2 / π
const real M_2_SQRTPI;
  2 / √π
const real SQRT2;
  √2
const real SQRT1_2;
  √½
real abs(real x);
long abs(long x);
int abs(int x);
real abs(creal z);
real abs(ireal y);
  Calculates the absolute value
  For complex numbers, abs(z) = sqrt( z.re2 + z.im2 ) = hypot(z.re, z.im).
creal conj(creal z);
ireal conj(ireal y);
  Complex conjugate
  conj(x + iy) = x - iy
  Note that z * conj(z) = z.re2 - z.im2 is always a real number
real cos(real x);
  Returns cosine of x. x is in radians.

  Special Values
  x | cos(x) | invalid?
  --- | --- | ---
  NAN | NAN | yes
  ±∞ | NAN | yes

  BUGS:
  Results are undefined if |x| >= 264.
real sin(real x);
  Returns sine of x. x is in radians.

  Special Values
  x | sin(x) | invalid?
  --- | --- | ---
  NAN | NAN | yes
  ±0.0 | ±0.0 | no
  ±∞ | NAN | yes

  BUGS:
  Results are undefined if |x| >= 264.
real tan(real x);
  Returns tangent of x. x is in radians.

  Special Values
  x | tan(x) | invalid?
  --- | --- | ---
  NAN | NAN | yes
  ±0.0 | ±0.0 | no
  ±∞ | NAN | yes

real acos(real x);
  Calculates the arc cosine of x, returning a value ranging from -π/2 to π/2.

  Special Values
  x | acos(x) | invalid?
  --- | --- | ---
  >1.0 | NAN | yes
  <-1.0 | NAN | yes
  NAN | NAN | yes

real asin(real x);
  Calculates the arc sine of x, returning a value ranging from -π/2 to π/2.

  Special Values
  x | asin(x) | invalid?
  --- | --- | ---
  ±0.0 | ±0.0 | no
  >1.0 | NAN | yes
  <-1.0 | NAN | yes

real atan(real x);
  Calculates the arc tangent of x, returning a value ranging from -π/2 to π/2.

  Special Values
  x | atan(x) | invalid?
  --- | --- | ---
  ±0.0 | ±0.0 | no
  ±∞ | NAN | yes

real atan2(real y, real x);
  Calculates the arc tangent of y / x, returning a value ranging from -π/2 to π/2.

  Special Values
  y | x | atan(y, x)
  --- | --- | ---
  NAN | anything | NAN
  anything | NAN | NAN
  ±0.0 | > 0.0 | ±0.0
  ±0.0 | ±0.0 | ±0.0
  ±0.0 | < 0.0 | ±π
  ±0.0 | -0.0 | ±π
  > 0.0 | ±0.0 | π/2
  < 0.0 | ±0.0 | π/2
  > 0.0 | ∞ | ±0.0
  ±∞ | anything | ±π/2
  > 0.0 | -∞ | ±π
  ±∞ | ∞ | ±π/4
  ±∞ | -∞ | ±3π/4

real cosh(real x);
  Calculates the hyperbolic cosine of x.

  Special Values
  x | cosh(x) | invalid?
  --- | --- | ---
  ±∞ | ±0.0 | no

real sinh(real x);
  Calculates the hyperbolic sine of x.

  Special Values
  x | sinh(x) | invalid?
  --- | --- | ---
  ±0.0 | ±0.0 | no
  ±∞ | ±∞ | no

real tanh(real x);
  Calculates the hyperbolic tangent of x.

  Special Values
  x | tanh(x) | invalid?
  --- | --- | ---
  ±0.0 | ±0.0 | no
  ±∞ | ±1.0 | no

real acosh(real x);
  Calculates the inverse hyperbolic cosine of x.
  Mathematically, acosh(x) = log(x + sqrt( x*x - 1))

  Special Values
  x | acosh(x)
  --- | ---
  NAN | NAN
  <1 | NAN
  1 | 0
  +∞ | +∞

real asinh(real x);
  Calculates the inverse hyperbolic sine of x.
  Mathematically,

        asinh(x) =  log( x + sqrt( x*x + 1 )) // if x >= +0
        asinh(x) = -log(-x + sqrt( x*x + 1 )) // if x <= -0

  Special Values
  x | asinh(x)
  --- | ---
  NAN | NAN
  ±0 | ±0
  ±∞ | ±∞

real atanh(real x);
  Calculates the inverse hyperbolic tangent of x, returning a value from ranging from -1 to 1.
  Mathematically, atanh(x) = log( (1+x)/(1-x) ) / 2

  Special Values
  x | acosh(x)
  --- | ---
  NAN | NAN
  ±0 | ±0
  -∞ | -0

long rndtol(real x);
  Returns x rounded to a long value using the current rounding mode. If the integer value of x is greater than long.max, the result is indeterminate.
real rndtonl(real x);
  Returns x rounded to a long value using the FE_TONEAREST rounding mode. If the integer value of x is greater than long.max, the result is indeterminate.
float sqrt(float x);
double sqrt(double x);
real sqrt(real x);
  Compute square root of x.

  Special Values
  x | sqrt(x) | invalid?
  --- | --- | ---
  -0.0 | -0.0 | no
  <0.0 | NAN | yes
  +∞ | +∞ | no

real exp(real x);
  Calculates ex.

  Special Values
  x | exp(x)
  --- | ---
  +∞ | +∞
  -∞ | +0.0

real exp2(real x);
  Calculates 2x.

  Special Values
  x | exp2(x)
  --- | ---
  +∞ | +∞
  -∞ | +0.0

real expm1(real x);
  Calculates the value of the natural logarithm base (e) raised to the power of x, minus 1.
  For very small x, expm1(x) is more accurate than exp(x)-1.

  Special Values
  x | ex-1
  --- | ---
  ±0.0 | ±0.0
  +∞ | +∞
  -∞ | -1.0

real frexp(real value, out int exp);
  Separate floating point value into significand and exponent.
  Returns:
  Calculate and return x and exp such that value =x*2exp and .5 <= |x| < 1.0
  x has same sign as value.

  Special Values
  value | returns | exp
  --- | --- | ---
  ±0.0 | ±0.0 | 0
  +∞ | +∞ | int.max
  -∞ | -∞ | int.min
  ±NAN | ±NAN | int.min

int ilogb(real x);
  Extracts the exponent of x as a signed integral value.
  If x is not a special value, the result is the same as `cast(int)logb(x)`.

  Special Values
  x | ilogb(x) | Range error?
  --- | --- | ---
  0 | FP_ILOGB0 | yes
  ±∞ | int.max | no
  NAN | FP_ILOGBNAN | no

real ldexp(real n, int exp);
  Compute n * 2exp
  References:
  frexp
real log(real x);
  Calculate the natural logarithm of x.

  Special Values
  x | log(x) | divide by 0? | invalid?
  --- | --- | --- | ---
  ±0.0 | -∞ | yes | no
  < 0.0 | NAN | no | yes
  +∞ | +∞ | no | no

real log10(real x);
  Calculate the base-10 logarithm of x.

  Special Values
  x | log10(x) | divide by 0? | invalid?
  --- | --- | --- | ---
  ±0.0 | -∞ | yes | no
  < 0.0 | NAN | no | yes
  +∞ | +∞ | no | no

real log1p(real x);
  Calculates the natural logarithm of 1 + x.
  For very small x, log1p(x) will be more accurate than log(1 + x).

  Special Values
  x | log1p(x) | divide by 0? | invalid?
  --- | --- | --- | ---
  ±0.0 | ±0.0 | no | no
  -1.0 | -∞ | yes | no
  <-1.0 | NAN | no | yes
  +∞ | -∞ | no | no

real log2(real x);
  Calculates the base-2 logarithm of x: log2x

  Special Values
  x | log2(x) | divide by 0? | invalid?
  --- | --- | --- | ---
  ±0.0 | -∞ | yes | no
  < 0.0 | NAN | no | yes
  +∞ | +∞ | no | no

real logb(real x);
  Extracts the exponent of x as a signed integral value.
  If x is subnormal, it is treated as if it were normalized. For a positive, finite x:

       1 <= x * FLT_RADIX-logb(x) < FLT_RADIX

  Special Values
  x | logb(x) | Divide by 0?
  --- | --- | ---
  ±∞ | +∞ | no
  ±0.0 | -∞ | yes

real modf(real x, ref real y);
  Calculates the remainder from the calculation x/y.
  Returns:
  The value of x - i * y, where i is the number of times that y can be completely subtracted from x. The result has the same sign as x.

  Special Values
  x | y | modf(x, y) | invalid?
  --- | --- | --- | ---
  ±0.0 | not 0.0 | ±0.0 | no
  ±∞ | anything | NAN | yes
  anything | ±0.0 | NAN | yes
  !=±∞ | ±∞ | x | no

real scalbn(real x, int n);
  Efficiently calculates x * 2n.
  scalbn handles underflow and overflow in the same fashion as the basic arithmetic operators.

  Special Values
  x | scalb(x)
  --- | ---
  ±∞ | ±∞
  ±0.0 | ±0.0

real cbrt(real x);
  Calculates the cube root x.

  Special Values
  x | cbrt(x) | invalid?
  --- | --- | ---
  ±0.0 | ±0.0 | no
  NAN | NAN | yes
  ±∞ | ±∞ | no

real fabs(real x);
  Returns |x|

  Special Values
  x | fabs(x)
  --- | ---
  ±0.0 | +0.0
  ±∞ | +∞

real hypot(real x, real y);
  Calculates the length of the hypotenuse of a right-angled triangle with sides of length x and y. The hypotenuse is the value of the square root of the sums of the squares of x and y:
  sqrt(x² + y²)
  Note that hypot(x, y), hypot(y, x) and hypot(x, -y) are equivalent.

  Special Values
  x | y | hypot(x, y) | invalid?
  --- | --- | --- | ---
  x | ±0.0 | |x| | no
  ±∞ | y | +∞ | no
  ±∞ | NAN | +∞ | no

real erf(real x);
  Returns the error function of x.
real erfc(real x);
  Returns the complementary error function of x, which is 1 - erf(x).
real lgamma(real x);
  Natural logarithm of gamma function.
  Returns the base e (2.718...) logarithm of the absolute value of the gamma function of the argument.
  For reals, lgamma is equivalent to log(fabs(gamma(x))).

  Special Values
  x | lgamma(x) | invalid?
  --- | --- | ---
  NAN | NAN | yes
  integer <= 0 | +∞ | yes
  ±∞ | +∞ | no

real tgamma(real x);
  The Gamma function, Γ(x)
  Γ(x) is a generalisation of the factorial function to real and complex numbers. Like x!, Γ(x+1) = x*Γ(x).
  Mathematically, if z.re > 0 then Γ(z) =∫0∞tz-1e-tdt

  Special Values
  x | Γ(x) | invalid?
  --- | --- | ---
  NAN | NAN | yes
  ±0.0 | ±∞ | yes
  integer > 0 | (x-1)! | no
  integer < 0 | NAN | yes
  +∞ | +∞ | no
  -∞ | NAN | yes

  References:
  http://en.wikipedia.org/wiki/Gamma_function, http://www.netlib.org/cephes/ldoubdoc.html#gamma
real ceil(real x);
  Returns the value of x rounded upward to the next integer (toward positive infinity).
real floor(real x);
  Returns the value of x rounded downward to the next integer (toward negative infinity).
real nearbyint(real x);
  Rounds x to the nearest integer value, using the current rounding mode.
  Unlike the rint functions, nearbyint does not raise the FE_INEXACT exception.
real rint(real x);
  Rounds x to the nearest integer value, using the current rounding mode. If the return value is not equal to x, the FE_INEXACT exception is raised. nearbyint performs the same operation, but does not set the FE_INEXACT exception.
long lrint(real x);
  Rounds x to the nearest integer value, using the current rounding mode.
real round(real x);
  Return the value of x rounded to the nearest integer. If the fractional part of x is exactly 0.5, the return value is rounded to the even integer.
long lround(real x);
  Return the value of x rounded to the nearest integer.
  If the fractional part of x is exactly 0.5, the return value is rounded away from zero.
real trunc(real x);
  Returns the integer portion of x, dropping the fractional portion.
  This is also known as "chop" rounding.
real remainder(real x, real y);
real remquo(real x, real y, out int n);
  Calculate the remainder x REM y, following IEC 60559.
  REM is the value of x - y * n, where n is the integer nearest the exact value of x / y. If |n - x / y| == 0.5, n is even. If the result is zero, it has the same sign as x. Otherwise, the sign of the result is the sign of x / y. Precision mode has no affect on the remainder functions.
  remquo returns n in the parameter n.

  Special Values
  x | y | remainder(x, y) | n | invalid?
  --- | --- | --- | --- | ---
  ±0.0 | not 0.0 | ±0.0 | 0.0 | no
  ±∞ | anything | NAN | ? | yes
  anything | ±0.0 | NAN | ? | yes
  != ±∞ | ±∞ | x | ? | no

int isnan(real e);
  Returns !=0 if e is a NaN.
int isfinite(real e);
  Returns !=0 if e is finite.
int isnormal(float x);
int isnormal(double d);
int isnormal(real e);
  Returns !=0 if x is normalized.
int issubnormal(float f);
int issubnormal(double d);
int issubnormal(real e);
  Is number subnormal? (Also called "denormal".) Subnormals have a 0 exponent and a 0 most significant mantissa bit.
int isinf(real e);
  Return !=0 if e is ±∞.
int signbit(real e);
  Return 1 if sign bit of e is set, 0 if not.
real copysign(real to, real from);
  Return a value composed of to with from's sign bit.
real nan(char[] tagp);
  Creates a quiet NAN with the information from tagp[] embedded in it.
real nextafter(real x, real y);
  Calculates the next representable value after x in the direction of y.
  If y > x, the result will be the next largest floating-point value; if y < x, the result will be the next smallest value. If x == y, the result is y. The FE_INEXACT and FE_OVERFLOW exceptions will be raised if x is finite and the function result is infinite. The FE_INEXACT and FE_UNDERFLOW exceptions will be raised if the function value is subnormal, and x is not equal to y.
real fdim(real x, real y);
  Returns the positive difference between x and y.
  Returns:

  x, y | fdim(x, y)
  --- | ---
  x > y | x - y
  x <= y | +0.0

real fmax(real x, real y);
  Returns the larger of x and y.
real fmin(real x, real y);
  Returns the smaller of x and y.
real fma(real x, real y, real z);
  Returns (x * y) + z, rounding only once according to the current rounding mode.
real pow(real x, uint n);
real pow(real x, int n);
  Fast integral powers.
real pow(real x, real y);
  Calculates x y.

  Special Values
  x | y | pow(x, y) | div 0 | invalid?
  --- | --- | --- | --- | ---
  anything | ±0.0 | 1.0 | no | no
  |x| > 1 | +∞ | +∞ | no | no
  |x| < 1 | +∞ | +0.0 | no | no
  |x| > 1 | -∞ | +0.0 | no | no
  |x| < 1 | -∞ | +∞ | no | no
  +∞ | > 0.0 | +∞ | no | no
  +∞ | < 0.0 | +0.0 | no | no
  -∞ | odd integer > 0.0 | -∞ | no | no
  -∞ | > 0.0, not odd integer | +∞ | no | no
  -∞ | odd integer < 0.0 | -0.0 | no | no
  -∞ | < 0.0, not odd integer | +0.0 | no | no
  ±1.0 | ±∞ | NAN | no | yes
  < 0.0 | finite, nonintegral | NAN | no | yes
  ±0.0 | odd integer < 0.0 | ±∞ | yes | no
  ±0.0 | < 0.0, not odd integer | +∞ | yes | no
  ±0.0 | odd integer > 0.0 | ±0.0 | no | no
  ±0.0 | > 0.0, not odd integer | +0.0 | no | no

int feqrel(real x, real y);
  To what precision is x equal to y?
  Returns:
  the number of mantissa bits which are equal in x and y. eg, 0x1.F8p+60 and 0x1.F1p+60 are equal to 5 bits of precision.

  Special Values
  x | y | feqrel(x, y)
  --- | --- | ---
  x | x | real.mant_dig
  x | >= 2*x | 0
  x | <= x/2 | 0
  NAN | any | 0
  any | NAN | 0

real poly(real x, real[] A);
  Evaluate polynomial A(x) = a0 + a1x + a2x² + a3x³ ...
  Uses Horner's rule A(x) = a0 + x(a1 + x(a2 + x(a3 + ...)))
  Params:

  real[] A | array of coefficients a0, a1, etc.

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