Data commit

Task/CRC-32/Icon/crc-32.icon

@@ -0,0 +1,33 @@
+link hexcvt,printf
+
+procedure main()
+   s := "The quick brown fox jumps over the lazy dog"
+   a := "414FA339"
+   printf("crc(%i)=%s - implementation is %s\n",
+          s,r := crc32(s),if r == a then "correct" else "in error")
+end
+
+procedure crc32(s)      #: return crc-32 (ISO 3309, ITU-T V.42, Gzip, PNG) of s
+static crcL,mask
+initial {
+   crcL := list(256)                            # crc table
+   p := [0,1,2,4,5,7,8,10,11,12,16,22,23,26]    # polynomial terms
+   mask := 2^32-1                               # word size mask
+   every (poly := 0) := ior(poly,ishift(1,31-p[1 to *p]))
+   every c := n := 0 to *crcL-1 do {            # table
+      every 1 to 8 do
+         c := iand(mask,
+                   if iand(c,1) = 1 then
+                      ixor(poly,ishift(c,-1))
+                   else
+                      ishift(c,-1)
+                  )
+      crcL[n+1] := c
+      }
+   }
+
+   crc := ixor(0,mask)                          # invert bits
+   every crc := iand(mask,
+                     ixor(crcL[iand(255,ixor(crc,ord(!s)))+1],ishift(crc,-8)))
+   return hexstring(ixor(crc,mask))             # return hexstring
+end