Implementing the SHA-1 hash algorithm
Python 3 - 645 chars

h=0x67452301,0xEFCDAB89,0x98BADCFE,0x10325476,0xC3D2E1F0
L=lambda v,s:(v&lt;&lt;s|v&gt;&gt;B-s)%2**B
B=32
R=range
m=input().encode()
l=len(m)
m+=b'\x80'+bytes((55-l)%64)+m.fromhex(hex(2**64+l*8)[3:])
for C in [m[i:i+64]for i in R(0,len(m),64)]:
 w=[sum(C[i+j]&lt;&lt;8*(3-j)for j in R(4))for i in R(0,64,4)];a,b,c,d,e=h
 for i in R(16,80):w+=[L(w[i-3]^w[i-8]^w[i-14]^w[i-16],1)]
 for i in R(80):f=[b&amp;c|~b&amp;d,b^c^d,b&amp;c|b&amp;d|c&amp;d,b^c^d][i//20];k=[0x5A827999,0x6ED9EBA1,0x8F1BBCDC,0xCA62C1D6][i//20];t=L(a,5)+f+e+k+w[i];e=d;d=c;c=L(b,30);b=a;a=t%2**32
 g=a,b,c,d,e;h=[(h[i]+g[i])%2**32for i in R(5)]
B=160
print('%x'%(L(h[0],128)|L(h[1],96)|L(h[2],64)|L(h[3],32)|h[4]))


Just a golfed version of the pseudocode.