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#define MAX_RANK 3
float2
philox (uint2 st,
uint k)
{
ulong p;
int i;
for (i = 0 ; i < 3 ; i += 1)
{
p = st.x * 0xcd9e8d57ul;
st.x = ((uint)(p >> 32)) ^ st.y ^ k;
st.y = (uint)p;
k += 0x9e3779b9u;
}
return convert_float2(st) / 2147483648.0f - 1.0f;
}
__kernel void kernel_noise (__global float *out,
const int x_0,
const int y_0,
const uint iterations,
const float scale,
const uint seed)
{
const int gidx = get_global_id(0);
const int gidy = get_global_id(1);
float c, d, m;
float2 p;
int j;
for (j = 0, m = 0, c = 1, d = scale;
j < iterations;
c *= 2, d *= 2, j += 1)
{
float s, t, n;
float2 g[3], u[3], i, di;
int k;
p = (float2)(gidx + x_0, gidy + y_0) * d;
/* Skew the input point and find the lowest corner of the containing
simplex. */
s = (p.x + p.y) * (sqrt(3.0f) - 1) / 2;
i = floor(p + s);
/* Calculate the (unskewed) distance between the input point and all
simplex corners. */
s = (i.x + i.y) * (3 - sqrt(3.0f)) / 6;
u[0] = p - i + s;
di = u[0].x >= u[0].y ? (float2)(1, 0) : (float2)(0, 1);
u[1] = u[0] - di + (3 - sqrt(3.0f)) / 6;
u[2] = u[0] - 1 + (3 - sqrt(3.0f)) / 3;
/* Calculate gradients for each corner vertex. We convert to
* signed int first to avoid implementation-defined behavior for
* out-of-range values. See section 6.2.3.3 of the OpenCL
* specification. */
g[0] = philox(convert_uint2(convert_int2(i)), seed);
g[1] = philox(convert_uint2(convert_int2(i + di)), seed);
g[2] = philox(convert_uint2(convert_int2(i + 1)), seed);
for (k = 0, n = 0 ; k < 3 ; k += 1)
{
t = 0.5f - dot(u[k], u[k]);
if (t > 0)
{
t *= t;
n += t * t * dot(g[k], u[k]);
}
}
m += 70 * n / c;
}
out[gidy * get_global_size(0) + gidx] = m;
}
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