From 5a25f07f8e5c7adc1a18d8f16f29a29ed4125166 Mon Sep 17 00:00:00 2001
From: Danny Robson <danny@nerdcruft.net>
Date: Wed, 25 Jan 2017 16:12:12 +1100
Subject: [PATCH] hash/crc: adapt implementation from png appendix

---
 CMakeLists.txt    |  1 +
 hash/crc.cpp      | 91 ++++++++++++++++++++++++++++-------------------
 hash/crc.hpp      |  7 +++-
 test/hash/crc.cpp | 40 +++++++++++++++++++++
 4 files changed, 101 insertions(+), 38 deletions(-)
 create mode 100644 test/hash/crc.cpp

diff --git a/CMakeLists.txt b/CMakeLists.txt
index 3dc3ebf3..f37f0ed9 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -464,6 +464,7 @@ if (TESTS)
         geom/aabb
         geom/ray
         hash/checksum
+        hash/crc
         hash/fasthash
         hash/hmac
         hash/hotp
diff --git a/hash/crc.cpp b/hash/crc.cpp
index 436771d7..8bc7b27b 100644
--- a/hash/crc.cpp
+++ b/hash/crc.cpp
@@ -18,13 +18,53 @@
 
 #include "../debug.hpp"
 
+#include <array>
+
 using util::hash::crc32;
 
 
 ///////////////////////////////////////////////////////////////////////////////
+static
+std::array<uint32_t,256>
+make_table (void)
+{
+    std::array<uint32_t,256> value {};
+
+    for (int i = 0; i < 256; ++i) {
+        std::uint32_t c = i;
+
+        for (int k = 0; k < 8; ++k) {
+            if (c & 1)
+                c = 0xEDB88320L ^ (c >> 1);
+            else
+                c >>= 1;
+        }
+
+        value[i] = c;
+    }
+
+    return value;
+};
+
+
+//-----------------------------------------------------------------------------
+static std::array<uint32_t,256> table = make_table ();
+
+
+///////////////////////////////////////////////////////////////////////////////
+crc32::crc32 () noexcept
+{
+    reset ();
+}
+
+
+//-----------------------------------------------------------------------------
 void
-crc32::reset (void)
-{ ; }
+crc32::reset (void) noexcept
+{
+    m_digest = 0;
+    m_digest = ~m_digest;
+}
 
 
 ///////////////////////////////////////////////////////////////////////////////
@@ -34,55 +74,32 @@ crc32::update (const uint8_t *restrict first,
 {
     CHECK_LE (first, last);
 
-    return update (first, last - first);
+    for (auto cursor = first; cursor != last; ++cursor) {
+        m_digest = table[*cursor ^ (m_digest & 0xFF)] ^ (m_digest >> 8u);
+    }
 }
 
 
 //-----------------------------------------------------------------------------
 void
-crc32::update (const void *restrict, size_t) noexcept
+crc32::update (const void *restrict _data, size_t len) noexcept
 {
-    not_implemented ();
-
-    /*
-    const uint8_t *restrict data = static_cast<const uint8_t*> (_data);
-    static const uint32_t POLYNOMIAL = hton (static_cast<uint32_t>(0x04C11DB7));
-
-    uint64_t bits = 0;
-    unsigned int i = 0;
-
-    if (size == 0)
-        return POLYNOMIAL;
-
-    switch (size) {
-        default:    bits |= static_cast<uint64_t>(data[3]) << 32U;
-        case 3:     bits |= static_cast<uint64_t>(data[2]) << 40U;
-        case 2:     bits |= static_cast<uint64_t>(data[1]) << 48U;
-        case 1:     bits |= static_cast<uint64_t>(data[0]) << 56U;
-    }
-
-    for (size_t i = 0; i < size; ++i) {
-        for (unsigned j = 0; j < 32; ++j) {
-            bool mix = bits 0x7000000000000000ULL;
-            bits <<= 1;
-
-            if (mix)
-                bits ^= POLYNOMIAL << 32;
-        }
-
-
-    }
-    */
+    auto data = reinterpret_cast<const uint8_t *restrict> (_data);
+    return update(data, data + len);
 }
 
 
 //-----------------------------------------------------------------------------
 void
 crc32::finish (void)
-{ not_implemented (); }
+{
+    ;
+}
 
 
 //-----------------------------------------------------------------------------
 typename crc32::digest_t
 crc32::digest (void) const
-{ not_implemented (); }
+{
+    return ~m_digest;
+}
\ No newline at end of file
diff --git a/hash/crc.hpp b/hash/crc.hpp
index 06106a80..4cf718f5 100644
--- a/hash/crc.hpp
+++ b/hash/crc.hpp
@@ -27,7 +27,9 @@ namespace util::hash {
     public:
         using digest_t = uint32_t;
 
-        void reset (void);
+        crc32 () noexcept;
+
+        void reset (void) noexcept;
 
         void update (const void *restrict data, size_t bytes) noexcept;
         void update (const uint8_t *restrict first, const uint8_t *restrict last) noexcept;
@@ -35,6 +37,9 @@ namespace util::hash {
         void finish (void);
 
         digest_t digest (void) const;
+
+    private:
+        digest_t m_digest;
     };
 }
 
diff --git a/test/hash/crc.cpp b/test/hash/crc.cpp
new file mode 100644
index 00000000..b6cd8cf6
--- /dev/null
+++ b/test/hash/crc.cpp
@@ -0,0 +1,40 @@
+#include "tap.hpp"
+#include "hash/crc.hpp"
+#include "hash/simple.hpp"
+
+#include <cstdint>
+#include <utility>
+#include <vector>
+
+
+///////////////////////////////////////////////////////////////////////////////
+static const
+struct {
+    uint32_t result;
+    const char *dat;
+    const char *msg;
+} TESTS[] = {
+    { 0x00000000, "",  "empty" },
+    { 0xe8b7be43, "a", "single letter" },
+    { 0xa684c7c6, "0123456789", "10 digits" },
+    { 0x414fa339, "The quick brown fox jumps over the lazy dog", "quick brown fox" },
+};
+
+
+///////////////////////////////////////////////////////////////////////////////
+int
+main (int, char**)
+{
+    util::TAP::logger tap;
+
+    for (const auto &t: TESTS) {
+        auto first = t.dat;
+        auto last  = first + strlen (t.dat);
+
+        auto result = util::hash::simple<util::hash::crc32> (first, last);
+
+        tap.expect_eq (t.result, result, "%s %xu", t.msg, result);
+    }
+
+    return tap.status ();
+}
\ No newline at end of file