k is just a constant array that is defined as the first 32 bits of the fractional parts of the cube roots of the first 64 primes from 2 to 311:
0x428a2f98, 0x71374491, 0xb5c0fbcf, 0xe9b5dba5, 0x3956c25b, 0x59f111f1, 0x923f82a4, 0xab1c5ed5,
0xd807aa98, 0x12835b01, 0x243185be, 0x550c7dc3, 0x72be5d74, 0x80deb1fe, 0x9bdc06a7, 0xc19bf174,
0xe49b69c1, 0xefbe4786, 0x0fc19dc6, 0x240ca1cc, 0x2de92c6f, 0x4a7484aa, 0x5cb0a9dc, 0x76f988da,
0x983e5152, 0xa831c66d, 0xb00327c8, 0xbf597fc7, 0xc6e00bf3, 0xd5a79147, 0x06ca6351, 0x14292967,
0x27b70a85, 0x2e1b2138, 0x4d2c6dfc, 0x53380d13, 0x650a7354, 0x766a0abb, 0x81c2c92e, 0x92722c85,
0xa2bfe8a1, 0xa81a664b, 0xc24b8b70, 0xc76c51a3, 0xd192e819, 0xd6990624, 0xf40e3585, 0x106aa070,
0x19a4c116, 0x1e376c08, 0x2748774c, 0x34b0bcb5, 0x391c0cb3, 0x4ed8aa4a, 0x5b9cca4f, 0x682e6ff3,
0x748f82ee, 0x78a5636f, 0x84c87814, 0x8cc70208, 0x90befffa, 0xa4506ceb, 0xbef9a3f7, 0xc67178f2
W is dynamically modified as follows:
1) W starts as an array or 64 32-bit words. Each chunk is copied into the first 16 words of this array. The rest of it doesn't matter, as it will get filled in the next step.
2) Elements 0-15 of w are filled. Let's fill in elements 16-63:
2a) Let's say we're filling in the i-th element. We calculate s0 as
(w[i-15]>>>7) xor (w[i-15]>>>18) xor (w[i-15] >>3)
2b) We calculate s1 as
(w[i-2]>>>17) xor (w[i-2]>>>19) xor (w[i-2]>>10)
2c) We set the i-th element to be
w[i-16] + s0 + w[i-7] + s1
>>> is a right rotation (elements pushed off the right are reinserted at the left)
>> is a right shift (no reinsertion at the left)
