#include pps/mathLib.tc
#include pps/library.tc

// md.tc - 2/15/15, 8/2,3,5/20 - lrb

[

This program reads files and outputs a "message digest." This is an 8
hexadecimal digit number created with a simple hashing algorithm. The
idea is two files which differ will with high probability generate
different message digests and two files that generate the same message
digest will with high probability be the same.

I learned about this from my friend Nhung Blaschke who was at the time a
peer tutor at Tunxis Community College. It was written in C++.

]

md char fn(0) [ // calculate message digest
	int s1, s2, s3, s4, m1, m2, m3, m4, i, bytes
	char b, a(8), where(5000)
	bytes = readfile fn, where, 5000
	m1 = 3; m2 = 7; m3 = 13; m4 = 23
	while i < bytes [
		b = where(i)
		s1 = (s1 + b * m1) % 256
		s2 = (s1 + s2 + b * m2) % 256
		s3 = (s1 + s2 + s3 + b * m3) % 256
		s4 = (s1 + s2 + s3 + s4 + b * m4) % 256
		i = i + 1
		]
	ctoh s1, a; ctoh s2, a + 2; ctoh s3, a + 4; ctoh s4, a + 6
	printf "%cMD value of %s is %s%c", 10, fn, a, 10
	]

main [
	char fn(40)
	printf "%cmd.tc - 8/5/20 - lrb%c", 10, 10
	printf "%cEnter file to process : ", 10; gs fn
	md fn
	]