Make SkSHA1 and SkM5 use common SkDigestHash result type

src/utils/SkHashDigest.h

Index: src/utils/SkHashDigest.h
===================================================================
--- src/utils/SkHashDigest.h	(revision 0)
+++ src/utils/SkHashDigest.h	(revision 0)
@@ -0,0 +1,149 @@
+/*
+ * Copyright 2013 Google Inc.
+ *
+ * Use of this source code is governed by a BSD-style license that can be
+ * found in the LICENSE file.
+ */
+
+#ifndef SkHashDigest_DEFINED
+#define SkHashDigest_DEFINED
+
+#include "SkData.h"
+#include "SkRefCnt.h"
+#include "SkString.h"
+
+/**
+ * A mutable hash digest; it can be filled with a bytearray of any
+ * length, anytime.
+ */
+class SkHashDigest {
+public:
+    SkHashDigest() : fSkDataRef(SkData::NewEmpty()) {}
+    SkHashDigest(const void *data, size_t length) : fSkDataRef(SkData::NewWithCopy(data, length)) {}
+
+    /**
+     * Destructor: if this object is the only one with a reference to the data
+     * that makes up the hash digest, then that data will be freed.
+     */
+    ~SkHashDigest() {
+    }
+
+    /**
+     * Replace the hash digest data held by this object with a copy of the
+     * data from this pointer/length.
+     */
+    void copyFrom(const void *data, size_t length) {
+        fSkDataRef = SkData::NewWithCopy(data, length);
+    }
+
+    /**
+     * Convert a single hexadecimal character [0-9a-fA-F] into its integer value
+     *
+     * @param c the hexadecimal character to convert
+     * @param result where the integer value will be written
+     * Returns true if the conversion succeeded.
+     */
+    static bool hexCharValue(const char c, uint8_t *result) {
+        if ((c >= '0') && (c <= '9')) {
+            *result = c - '0';
+        } else if ((c >= 'a') && (c <= 'f')) {
+            *result = c - ('a' - 10);
+        } else if ((c >= 'A') && (c <= 'F')) {
+            *result = c - ('A' - 10);
+        } else {
+            // EPOGER: add unittest that exercises this
+            SkDEBUGF(("unrecognized hexChar '%c'\n", c));
+            return false;
+        }
+        return true;
+    }
+
+    /**
+     * Fill in the hash digest data from a null-terminated hexadecimal string.
+     *
+     * Returns true if it was able to properly parse the hexadecimal string.
+     */
+    bool copyFromHexString(const char *hexString) {
+        const int stringLen = strlen(hexString);
+        if (0 != stringLen % 2) {
+            // EPOGER: add unittest that exercises this
+            SkDEBUGF(("hexString '%s' has odd length %d\n", hexString, stringLen));
+            return false;
+        }
+        const int digestLen = stringLen / 2;
+
+        // EPOGER: rewrite in a way that doesn't need this temporary array and memcpy?
+        uint8_t digest[digestLen];
+        uint8_t *digestPtr = digest;
+        uint8_t *pastDigestEnd = digest + digestLen;
+        const char *hexStringPtr = hexString;
+        while (digestPtr < pastDigestEnd) {
+            uint8_t nybble1, nybble2;
+            if (!hexCharValue(*hexStringPtr++, &nybble1)) {
+                return false;
+            }
+            if (!hexCharValue(*hexStringPtr++, &nybble2)) {
+                return false;
+            }
+            *digestPtr++ = (nybble1 << 4) + nybble2;
+        }
+
+        this->copyFrom(digest, digestLen);
+        return true;
+    }
+
+    /**
+     * Return a pointer to the SkData object holding the hash digest data.
+     *
+     * The SkData object's reference counter will be bumped to account for this call,
+     * so the caller must call unref() on it once it is no longer needed!
+     *
+     * For example:
+     *   {
+     *     SkData *skDataPtr = digest.skDataPtr();
+     *     const uint8_t* bytes = skDataPtr->bytes();
+     *     ...
+     *     skDataPtr->unref();
+     *   }
+     */
+    // EPOGER: try to set it up so that this is never needed, and the caller would just ask for a string representation instead???
+    SkData *skDataPtr() const {
+        return fSkDataRef.get();
+    }
+
+    size_t size() const {
+        return fSkDataRef->size();
+    }
+
+    bool equals(const SkHashDigest &other) const {
+        return fSkDataRef->equals(other.fSkDataRef.get());
+    }
+    friend bool operator==(const SkHashDigest& a, const SkHashDigest& b) {
+        return a.equals(b);
+    }
+
+    /**
+     * Returns a printable SkString representation of the hash digest
+     * (the bytes in hexadecimal, e.g. "deadbeef49")
+     */
+    SkString toHexString() const {
+        SkString retval;
+        const uint8_t *start = fSkDataRef->bytes();
+        const uint8_t *pastTheEnd = start + fSkDataRef->size();
+        for (const uint8_t *b = start; b < pastTheEnd; b++) {
+            // EPOGER: faster implementation that doesn't use appendf()?
+            retval.appendf("%02x", *b);
+        }
+        return retval;
+    }
+
+private:
+
+    // The SkData pointer within fSkDataRef may change over the
+    // lifetime of the SkHashDigest object, but it will never be set
+    // to NULL.  (Every SkHashDigest constructor initializes it to
+    // point at *some* SkData object.)
+    SkRefPtr<SkData> fSkDataRef;
+};
+
+#endif