direct implementation of simplex and perlin noise in C, no optimizations, allowing for speed comparison.

comparenoise.c

#include <stdio.h>
#include <stdlib.h>
#include <math.h>

int grad3[12][3] = {{1,1,0},{-1,1,0},{1,-1,0},{-1,-1,0},
                             {1,0,1},{-1,0,1},{1,0,-1},{-1,0,-1},
                             {0,1,1},{0,-1,1},{0,1,-1},{0,-1,-1}};

int p[] = {151,160,137,91,90,15,
                131,13,201,95,96,53,194,233,7,225,140,36,103,30,69,142,8,99,37,240,21,10,23,
                190, 6,148,247,120,234,75,0,26,197,62,94,252,219,203,117,35,11,32,57,177,33,
                88,237,149,56,87,174,20,125,136,171,168, 68,175,74,165,71,134,139,48,27,166,
                77,146,158,231,83,111,229,122,60,211,133,230,220,105,92,41,55,46,245,40,244,
                102,143,54, 65,25,63,161, 1,216,80,73,209,76,132,187,208, 89,18,169,200,196,
                135,130,116,188,159,86,164,100,109,198,173,186, 3,64,52,217,226,250,124,123,
                5,202,38,147,118,126,255,82,85,212,207,206,59,227,47,16,58,17,182,189,28,42,
                223,183,170,213,119,248,152, 2,44,154,163, 70,221,153,101,155,167, 43,172,9,
                129,22,39,253, 19,98,108,110,79,113,224,232,178,185, 112,104,218,246,97,228,
                251,34,242,193,238,210,144,12,191,179,162,241, 81,51,145,235,249,14,239,107,
                49,192,214, 31,181,199,106,157,184, 84,204,176,115,121,50,45,127, 4,150,254,
                138,236,205,93,222,114,67,29,24,72,243,141,128,195,78,66,215,61,156,180};

int perm[512];


/* This method is a *lot* faster than using (int)Math.floor(x) */
int fastfloor(double x) {
    return x>0 ? (int)x : (int)x-1;
}
 
double dot2d(int g[3], double x, double y) {
    return g[0]*x + g[1]*y; 
}

double dot3d(int g[3], double x, double y, double z) {
    return g[0]*x + g[1]*y + g[2]*z;
}

double mix(double a, double b, double t) {
    return (1-t)*a + t*b;
}

double fade(double t) {
    return t*t*t*(t*(t*6-15)+10);
}

/* Classic Perlin noise, 3D version */
double classic_noise(double x, double y, double z) {
    /* Find unit grid cell containing point */
    int X = fastfloor(x);
    int Y = fastfloor(y);
    int Z = fastfloor(z);
    /* Get relative xyz coordinates of point within that cell */
    x = x - X;
    y = y - Y;
    z = z - Z;
    /* Wrap the integer cells at 255 (smaller integer period can be introduced here) */
    X = X & 255;
    Y = Y & 255;
    Z = Z & 255;
    /* Calculate a set of eight hashed gradient indices */
    int gi000 = perm[X+perm[Y+perm[Z]]] % 12;
    int gi001 = perm[X+perm[Y+perm[Z+1]]] % 12;
    int gi010 = perm[X+perm[Y+1+perm[Z]]] % 12; 
    int gi011 = perm[X+perm[Y+1+perm[Z+1]]] % 12;
    int gi100 = perm[X+1+perm[Y+perm[Z]]] % 12;
    int gi101 = perm[X+1+perm[Y+perm[Z+1]]] % 12;
    int gi110 = perm[X+1+perm[Y+1+perm[Z]]] % 12;
    int gi111 = perm[X+1+perm[Y+1+perm[Z+1]]] % 12;
    /* The gradients of each corner are now:
        * g000 = grad3[gi000];
        * g001 = grad3[gi001];
        * g010 = grad3[gi010];
        * g011 = grad3[gi011];
        * g100 = grad3[gi100];
        * g101 = grad3[gi101];
        * g110 = grad3[gi110];
        * g111 = grad3[gi111]; */
    /* Calculate noise contributions from each of the eight corners */
    double n000= dot3d(grad3[gi000], x, y, z);
    double n100= dot3d(grad3[gi100], x-1, y, z);
    double n010= dot3d(grad3[gi010], x, y-1, z);
    double n110= dot3d(grad3[gi110], x-1, y-1, z);
    double n001= dot3d(grad3[gi001], x, y, z-1);
    double n101= dot3d(grad3[gi101], x-1, y, z-1);
    double n011= dot3d(grad3[gi011], x, y-1, z-1);
    double n111= dot3d(grad3[gi111], x-1, y-1, z-1);
    /* Compute the fade curve value for each of x, y, z */
    double u = fade(x);
    double v = fade(y);
    double w = fade(z);
     /* Interpolate along x the contributions from each of the corners */
    double nx00 = mix(n000, n100, u);
    double nx01 = mix(n001, n101, u);
    double nx10 = mix(n010, n110, u);
    double nx11 = mix(n011, n111, u);
    /* Interpolate the four results along y */
    double nxy0 = mix(nx00, nx10, v);
    double nxy1 = mix(nx01, nx11, v);
    /* Interpolate the two last results along z */
    double nxyz = mix(nxy0, nxy1, w);
    return nxyz;
}

/* 2D simplex noise */
double simplex_noise_2d(double xin, double yin) {
    double n0, n1, n2; 
    /* Noise contributions from the three corners */
    /* Skew the input space to determine which simplex cell we're in */
    double F2 = 0.5*(sqrt(3.0)-1.0);
    double s = (xin+yin)*F2; 
    /* Hairy factor for 2D */
    int i = fastfloor(xin+s);
    int j = fastfloor(yin+s);
    double G2 = (3.0-sqrt(3.0))/6.0;
    double t = (i+j)*G2;
    double X0 = i-t; 
    /* Unskew the cell origin back to (x,y) space */
    double Y0 = j-t;
    double x0 = xin-X0; 
    /* The x,y distances from the cell origin */
    double y0 = yin-Y0;
    /* For the 2D case, the simplex shape is an equilateral triangle.*/
    /* Determine which simplex we are in. */
    int i1, j1; 
    /* Offsets for second (middle) corner of simplex in (i,j) coords */
    if(x0>y0) {i1=1; j1=0;} 
    /* lower triangle, XY order: (0,0)->(1,0)->(1,1) */
    else {i1=0; j1=1;}      
    /* upper triangle, YX order: (0,0)->(0,1)->(1,1) */
    /* A step of (1,0) in (i,j) means a step of (1-c,-c) in (x,y), and */
    /* a step of (0,1) in (i,j) means a step of (-c,1-c) in (x,y), where */
    /* c = (3-sqrt(3))/6 */
    double x1 = x0 - i1 + G2; 
    /* Offsets for middle corner in (x,y) unskewed coords */
    double y1 = y0 - j1 + G2;
    double x2 = x0 - 1.0 + 2.0 * G2; 
    /* Offsets for last corner in (x,y) unskewed coords */
    double y2 = y0 - 1.0 + 2.0 * G2;
    /* Work out the hashed gradient indices of the three simplex corners */
    int ii = i & 255;
    int jj = j & 255;
    int gi0 = perm[ii+perm[jj]] % 12;
    int gi1 = perm[ii+i1+perm[jj+j1]] % 12;
    int gi2 = perm[ii+1+perm[jj+1]] % 12;
    /* Calculate the contribution from the three corners */
    double t0 = 0.5 - x0*x0-y0*y0;
    if(t0<0) n0 = 0.0;
    else {
        t0 *= t0;
        n0 = t0 * t0 * dot2d(grad3[gi0], x0, y0);  
        /* (x,y) of grad3 used for 2D gradient */
    }
    double t1 = 0.5 - x1*x1-y1*y1;
    if(t1<0) n1 = 0.0;
    else {
        t1 *= t1;
        n1 = t1 * t1 * dot2d(grad3[gi1], x1, y1);
    }
    double t2 = 0.5 - x2*x2-y2*y2;
    if(t2<0) n2 = 0.0;
    else {
        t2 *= t2;
        n2 = t2 * t2 * dot2d(grad3[gi2], x2, y2);
    }
    /* Add contributions from each corner to get the final noise value. */
    /* The result is scaled to return values in the interval [-1,1]. */
    return 70.0 * (n0 + n1 + n2);
}

/* 3D simplex noise */
double simplex_noise_3d(double xin, double yin, double zin) 
{
    double n0, n1, n2, n3; 
    /* Noise contributions from the four corners */
    /* Skew the input space to determine which simplex cell we're in */
    double F3 = 1.0/3.0;
    double s = (xin+yin+zin)*F3; 
    /* Very nice and simple skew factor for 3D */
    int i = fastfloor(xin+s);
    int j = fastfloor(yin+s);
    int k = fastfloor(zin+s);
    double G3 = 1.0/6.0; 
    /* Very nice and simple unskew factor, too */
    double t = (i+j+k)*G3; 
    double X0 = i-t; 
    /* Unskew the cell origin back to (x,y,z) space */
    double Y0 = j-t;
    double Z0 = k-t;
    double x0 = xin-X0; 
    /* The x,y,z distances from the cell origin */
    double y0 = yin-Y0;
    double z0 = zin-Z0;
    /* For the 3D case, the simplex shape is a slightly irregular tetrahedron. */
    /* Determine which simplex we are in. */
    int i1, j1, k1; 
    /* Offsets for second corner of simplex in (i,j,k) coords */
    int i2, j2, k2; 
    /* Offsets for third corner of simplex in (i,j,k) coords */
    if(x0>=y0) {
        if(y0>=z0)
        { i1=1; j1=0; k1=0; i2=1; j2=1; k2=0; } 
        /* X Y Z order */
        else if(x0>=z0) { i1=1; j1=0; k1=0; i2=1; j2=0; k2=1; } 
        /* X Z Y order */
        else { i1=0; j1=0; k1=1; i2=1; j2=0; k2=1; } 
        /* Z X Y order */
    }
    else { 
        /* x0<y0 */
        if(y0<z0) { i1=0; j1=0; k1=1; i2=0; j2=1; k2=1; } 
        /* Z Y X order */
        else if(x0<z0) { i1=0; j1=1; k1=0; i2=0; j2=1; k2=1; } 
        /* Y Z X order */
        else { i1=0; j1=1; k1=0; i2=1; j2=1; k2=0; } 
        /* Y X Z order */
    }
    /* A step of (1,0,0) in (i,j,k) means a step of (1-c,-c,-c) in (x,y,z), */
    /* a step of (0,1,0) in (i,j,k) means a step of (-c,1-c,-c) in (x,y,z), and */
    /* a step of (0,0,1) in (i,j,k) means a step of (-c,-c,1-c) in (x,y,z), where */
    /* c = 1/6. */
    double x1 = x0 - i1 + G3; 
    /* Offsets for second corner in (x,y,z) coords */
    double y1 = y0 - j1 + G3;
    double z1 = z0 - k1 + G3;
    double x2 = x0 - i2 + 2.0*G3; 
    /* Offsets for third corner in (x,y,z) coords */
    double y2 = y0 - j2 + 2.0*G3;
    double z2 = z0 - k2 + 2.0*G3;
    double x3 = x0 - 1.0 + 3.0*G3; 
    /* Offsets for last corner in (x,y,z) coords */
    double y3 = y0 - 1.0 + 3.0*G3;
    double z3 = z0 - 1.0 + 3.0*G3;
    /* Work out the hashed gradient indices of the four simplex corners */
    int ii = i & 255;
    int jj = j & 255;
    int kk = k & 255;
    int gi0 = perm[ii+perm[jj+perm[kk]]] % 12;
    int gi1 = perm[ii+i1+perm[jj+j1+perm[kk+k1]]] % 12;
    int gi2 = perm[ii+i2+perm[jj+j2+perm[kk+k2]]] % 12;
    int gi3 = perm[ii+1+perm[jj+1+perm[kk+1]]] % 12;
    /* Calculate the contribution from the four corners */
    double t0 = 0.6 - x0*x0 - y0*y0 - z0*z0;
    if(t0<0) n0 = 0.0;
    else {
        t0 *= t0;
        n0 = t0 * t0 * dot3d(grad3[gi0], x0, y0, z0);
    }
    double t1 = 0.6 - x1*x1 - y1*y1 - z1*z1;
    if(t1<0) n1 = 0.0;
    else {
        t1 *= t1;
        n1 = t1 * t1 * dot3d(grad3[gi1], x1, y1, z1);
    }
    double t2 = 0.6 - x2*x2 - y2*y2 - z2*z2;
    if(t2<0) n2 = 0.0;
    else {
        t2 *= t2;
        n2 = t2 * t2 * dot3d(grad3[gi2], x2, y2, z2);
    }
    double t3 = 0.6 - x3*x3 - y3*y3 - z3*z3;
    if(t3<0) n3 = 0.0;
    else {
        t3 *= t3;
        n3 = t3 * t3 * dot3d(grad3[gi3], x3, y3, z3);
    }
    /* Add contributions from each corner to get the final noise value. */
    /* The result is scaled to stay just inside [-1,1] */
    return 32.0*(n0 + n1 + n2 + n3);
}

int main( int argc, char *argv[] ) {
    int num_points = 500; /* how many points to calculate, in each direction! */
    int i, j, k;
    int noise_type = 1; /* default to 3d simplex. */

    if ( argc != 2 ) {
        printf( "usage: %s <noise_type>\n noise types: \n\t1 -> classic noise\n\t2 -> 2d simplex\n\t3 -> 3d simplex \n", argv[ 0 ] );
        return 1;
    }
    else {
        noise_type = *argv[ 1 ];
    }

    /* To remove the need for index wrapping, double the permutation table length */
    for ( i = 0; i < 512; i++) {
        perm[ i ] = p[ i & 255 ]; 
    }

    if ( noise_type == '1' ) { /* classic 3d perlin noise. */
        for ( k = 0; k < num_points; k++ ) {
            for ( j = 0; j < num_points; j++ ) {
                for ( i = 0; i < num_points; i++ ) {
                    double noise = classic_noise( i / 8.0, j / 8.0, k / 8.0 );
                    noise = noise * 1.0; /* dummy noop to avoid compile warning. */
                }
            }
        }
    }
    else if ( noise_type == '2' ) { /* 2d simplex noise. */
        for ( j = 0; j < num_points * num_points; j++ ) { /* make up for being in a 2d plane by doing more */
            for ( i = 0; i < num_points; i++ ) {
                double noise = simplex_noise_2d( i / 8.0, j / 8.0 );
                    noise = noise * 1.0; /* dummy noop to avoid compile warning. */
            }
        }
    }
    else if ( noise_type == '3' ) { /* 3d simplex noise. */
        for ( k = 0; k < num_points; k++ ) {
            for ( j = 0; j < num_points; j++ ) {
                for ( i = 0; i < num_points; i++ ) {
                    double noise = simplex_noise_3d( i / 8.0, j / 8.0, k / 8.0 );
                    noise = noise * 1.0; /* dummy noop to avoid compile warning. */
                }
            }
        }
    }
    else {
        printf( "unknown noise type.\n" );
        return 2;
    }

    return 0;
}