Module Gg.Float

Floating point number utilities.

This module defines a few useful constants, functions, predicates and comparisons on floating point numbers. The printers output a lossless textual representation of floats.

Quick recall on OCaml's floating point representation.

type t = float

The type for floating point numbers.

Constants

val e : float

The constant e.

val pi : float

The constant pi.

val two_pi : float

2 *. pi

val pi_div_2 : float

pi /. 2.

val pi_div_4 : float

pi /. 4.

val inv_pi : float

1 /. pi.

val max_sub_float : float

The greatest positive subnormal floating point number.

val min_sub_float : float

The smallest positive subnormal floating point number.

val max_frac_float : float

The greatest positive floating point number with a fractional part (the float before 252). Any number outside [-max_frac_float;max_frac_float] is an integer.

val max_int_arith : float

The greatest positive floating point number (253) such that any integer in the range [-max_int_arith;max_int_arith] is represented exactly. Integer arithmetic can be performed exactly in this interval.

Functions

Note. If applicable, a function taking NaNs returns a NaN unless otherwise specified.

val deg_of_rad : float -> float

deg_of_rad r is r radians in degrees.

val rad_of_deg : float -> float

rad_of_deg d is d degrees in radians.

val wrap_angle : float -> float

wrap_angle r is the angle r in the interval [-pi;pi[.

val random : ?min:float -> len:float -> unit -> float

random min len () is a random float in the interval [min;min+len] (min defaults to 0.). Uses the standard library's default Random state for the generation.

Warning. The float generated by a given state may change in future versions of the library.

val srandom : Random.State.t -> ?min:float -> len:float -> unit -> float

srandom state min len () is like random but uses state for the generation.

Warning. The float generated by a given state may change in future versions of the library.

val mix : float -> float -> float -> float

mix x y t is the linear interpolation x +. t *. (y -. x).

val step : float -> float -> float

step edge x is 0. if x < edge and 1. otherwise. The result is undefined on NaNs.

val smooth_step : float -> float -> float -> float

smooth_step e0 e1 x is 0. if x <= e0, 1. if x >= e1 and cubic hermite interpolation between 0. and 1. otherwise. The result is undefined on NaNs.

val fmax : float -> float -> float

fmax x y is y if x < y and x otherwise. If x or y is NaN returns the other argument. If both are NaNs returns NaN.

val fmin : float -> float -> float

fmin x y is x if x < y and y otherwise. If x or y is NaN returns the other argument. If both are NaNs returns NaN.

val clamp : min:float -> max:float -> float -> float

clamp min max x is min if x < min, max if x > max and x otherwise. The result is undefined on NaNs and if min > max.

val remap : x0:float -> x1:float -> y0:float -> y1:float -> float -> float

remap x0 x1 y0 y1 v applies to v the affine transform that maps x0 to y0 and x1 to y1. If the transform is undefined (x0 = x1 and y0 <> y1) the function returns y0 for any v.

val round : float -> float

round x is the integer nearest to x. Ties are rounded towards positive infinity. If x is an infinity, returns x.

Note. If the absolute magnitude of x is an integer strictly greater than max_frac_float, round x = x may be false.

val int_of_round : float -> int

int_of_round x is truncate (round v). The result is undefined on NaNs and infinities.

val round_dfrac : int -> float -> float

round_dfrac d x rounds x to the dth decimal fractional digit. Ties are rounded towards positive infinity. If x is an infinity, returns x. The result is only defined for 0 <= d <= 16.

val round_dsig : int -> float -> float

round_dsig d x rounds the normalized decimal significand of x to the dth decimal fractional digit. Ties are rounded towards positive infinity. The result is NaN on infinities. The result only defined for 0 <= d <= 16.

Warning. The current implementation overflows on large x and d.

val round_zero : eps:float -> float -> float

round_zero eps x is 0. if abs_float x < eps and x otherwise. The result is undefined if eps is NaN.

val chop : eps:float -> float -> float

chop eps x is round x if abs_float (x -. round x) < eps and x otherwise. The result is undefined if eps is NaN.

val sign : float -> float

sign x is 1. if x > 0., 0. if x = 0., -1. if x < 0.

val sign_bit : float -> bool

sign_bit x is true iff the sign bit is set in x.

val succ : float -> float

succ x is the floating point value just after x towards positive infinity. Returns in particular :

  • NaN on NaNs.
  • infinity on infinity.
  • -max_float on neg_infinity.
  • min_sub_float on 0. or -0..
val pred : float -> float

pred x is -. succ (-.x), i.e. the floating point value before x towards negative infinity.

val nan : int -> float

nan payload is a NaN whose 51 lower significand bits are defined by the 51 lower (or less, as int allows) bits of payload.

val nan_payload : float -> int

nan_payload x is the 51 lower significand bits (or less, as int allows) of the NaN x.

  • raises Invalid_argument

    if x is not a NaN.

Predicates and comparisons

val is_zero : eps:float -> float -> bool

is_zero eps x is true if abs_float x < eps and false otherwise. The result is undefined if eps is NaN.

val is_nan : float -> bool

is_nan x is true iff x is a NaN.

val is_inf : float -> bool

is_inf x is true iff x is infinity or neg_infinity.

val is_int : float -> bool

is_int x is true iff x is an integer.

val equal : float -> float -> bool

equal x y is x = y.

val equal_tol : eps:float -> float -> float -> bool

equal_tol eps x y is true iff |x - y| <= eps * max (1,|x|,|y|). On special values the function behaves like compare x y = 0. The condition turns into an absolute tolerance test for small magnitudes and a relative tolerance test for large magnitudes.

val compare : float -> float -> int

compare x y is Pervasives.compare x y.

val compare_tol : eps:float -> float -> float -> int

compare_tol ~eps x y is 0 iff equal_tol ~eps x y is true and Pervasives.compare x y otherwise.

Printers

val pp : Format.formatter -> float -> unit

pp ppf x prints a lossless textual representation of x on ppf.

  • Normals are represented by "[-]0x1.<f>p<e>" where <f> is the significand bits in hexadecimal and <e> the unbiased exponent in decimal.
  • Subnormals are represented by "[-]0x0.<f>p-1022" where <f> is the significand bits in hexadecimal.
  • NaNs are represented by "[-]nan(0x<p>)" where <p> is the payload in hexadecimal.
  • Infinities and zeroes are represented by "[-]inf" and "[-]0.".

This format should be compatible with recent implementations of strtod and hence with float_of_string (but negative NaNs seem to be problematic to get back).

Quick recall on OCaml's floats

An OCaml float is an IEEE-754 64 bit double precision binary floating point number. The 64 bits are laid out as follows :

+----------------+-----------------------+-------------------------+
| sign s (1 bit) | exponent e (11 bits)  | significand t (52 bits) |
+----------------+-----------------------+-------------------------+
               63|62                   52|51                      0|

The value represented depends on s, e and t :

sign   exponent       significand   value represented           meaning
-------------------------------------------------------------------------
s      0              0             -1^s * 0                    zero
s      0              t <> 0        -1^s * 0.t * 2^-1022        subnormal
s      0 < e < 2047   f             -1^s * 1.t * 2^(e - 1023)   normal
s      2047           0             -1^s * infinity             infinity
s      2047           t <> 0        NaN                         not a number

There are two zeros, a positive and a negative one but both are deemed equal by = and Pervasives.compare. A NaN is never equal (=) to itself or to another NaN however Pervasives.compare asserts any NaN to be equal to itself and to any other NaN.

The bit layout of a float can be converted to an int64 and back using Int64.bits_of_float and Int64.float_of_bits.

The bit 51 of a NaN is used to distinguish between quiet (bit set) and signaling NaNs (bit cleared); the remaining 51 lower bits of the significand are the NaN's payload which can be used to store diagnostic information. These features don't seem to used in OCaml.

The significand of a floating point number is made of 53 binary digits (don't forget the implicit digit), this corresponds to log10(253) ~ 16 decimal digits.

Only float values in the interval ]-252;252[ may have a fractional part. Float.max_frac_float is the greatest positive float with a fractional part.

Any integer value in the interval [-253;253] can be represented exactly by a float value. Integer arithmetic performed in this interval is exact. Float.max_int_arith is 253.