raisim::noiseUtils

class · #include <raisim/Terrain.hpp>

Internal: numeric helpers of the terrain noise generator.

Static member functions

fastFloor static

static std::int64_t fastFloor(double f) noexcept

Floor as a SIGNED integer. Returning an unsigned type would wrap every negative result to ~1.8e19, which breaks x -= fastFloor(x) in PerlinNoise::sample below. Truncation toward zero already equals floor for f >= 0 and for exact negative integers; only a negative value with a fractional part needs the extra -1.

Parameters

Parameter	Description
f (in)	value inside the int64 range

Returns floor(f)

fastRound static

static std::int64_t fastRound(double f) noexcept

Parameters

Parameter	Description
f (in)	value

Returns f rounded to the nearest integer, halves away from zero

map static

static double map(
    double value,
    double lower0,
    double upper0,
    double lower1,
    double upper1)

Linearly maps value from [lower0, upper0] to [lower1, upper1] (no clamping).

Parameters

Parameter	Description
value (in)	input value
lower0 (in)	input range start
upper0 (in)	input range end
lower1 (in)	output range start
upper1 (in)	output range end

Returns the mapped value

uniformBelow static

static std::uint64_t uniformBelow(std::mt19937 &engine, std::uint64_t bound)

A uniform integer below a bound, drawn from the engine as std::uniform_int_distribution of libstdc++ draws it (see kMultiplyShiftReduction), with any standard library.

Parameters

Parameter	Description
engine (in, out)	the generator
bound (in)	exclusive upper bound, in [1, 2^32)

Returns the draw, in [0, bound)

shuffle static

template <typename T>
static void shuffle(T *values, std::uint64_t count, std::mt19937 &engine)

Permute values[0, count) as std::shuffle(values, values + count, engine) does in libstdc++. The standard leaves that permutation to the library, so libc++ and the Microsoft library permuted the same values differently from the same seed. Each draw of the engine gives the swap partners of two consecutive elements.

Parameters

Parameter	Description
values (in, out)	the values
count (in)	number of values, in [1, 65535]
engine (in, out)	the generator

Public attributes

kMultiplyShiftReduction

static constexpr bool kMultiplyShiftReduction

How uniformBelow() reduces a 32-bit draw to a bound. false: libstdc++ 10 (the toolchain of the released Linux binaries) rejects draws past the largest multiple of the bound and divides. true: libstdc++ 11 and newer take the high half of the draw times the bound and reject the low halves below 2^32 mod bound (Lemire, "Fast Random Integer Generation in an Interval", 2019).