Add simple CRC32 functions

ReadMe.org

@@ -106,6 +106,7 @@ Here are the known compatibility results, where blank means untested/unknown:
 | FileDialog.cake             | Yes          | Yes          | Yes         |       |
 | FileSystem.cake             | Yes          | Yes          | Yes         |       |
 | FreeType.cake               | Yes          |              |             |       |
+| Hash.cake                   | Yes          | Yes          | Yes         | Yes   |
 | Image.cake                  | Yes          | Yes          | Yes         |       |
 | ImGui.cake                  | Yes          | No[1]        | Yes         |       |
 | ImGuiSDLOpenGL.cpp          | Yes          | No[1]        | Yes         |       |

src/Hash.cake

@@ -0,0 +1,28 @@
+(c-import
+ "<assert.h>"
+ &with-decls "<stdint.h>" "<stddef.h>")
+
+;; From http://home.thep.lu.se/~bjorn/crc/ (public domain)
+(defun-local hash-crc32-for-byte (r uint32_t &return uint32_t)
+  (each-in-range 8 j
+	(set r (bit-xor
+            (? (bit-and r 1) 0
+               (type-cast 0xEDB88320L uint32_t))
+            (bit->> r 1))))
+  (return (bit-xor r (type-cast 0xFF000000L uint32_t))))
+
+(var s-crc32-table ([] 0x100 uint32_t))
+(defun hash-crc32-initialize ()
+  (each-in-range 0x100 i
+	(set (at i s-crc32-table) (hash-crc32-for-byte i))))
+
+(defun hash-crc32 (data (* (const void)) n-bytes size_t crc-out (* uint32_t))
+  (unless (deref s-crc32-table)
+	(assert (and s-crc32-table "Need to call crc32-initialize first")))
+  (each-in-range n-bytes i
+	(set (deref crc-out)
+         (bit-xor
+          (at (bit-xor (type-cast (deref crc-out) uint8_t)
+                       (at i (type-cast data (* uint8_t))))
+              s-crc32-table)
+          (bit->> (deref crc-out) 8)))))