michael@0: /* -*- Mode: C++; tab-width: 2; indent-tabs-mode: nil; c-basic-offset: 2 -*- */
michael@0: /* This Source Code Form is subject to the terms of the Mozilla Public
michael@0:  * License, v. 2.0. If a copy of the MPL was not distributed with this
michael@0:  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
michael@0: 
michael@0: #include "prlog.h"
michael@0: #include "nsEntropyCollector.h"
michael@0: #include "nsAlgorithm.h"
michael@0: #include <algorithm>
michael@0: 
michael@0: nsEntropyCollector::nsEntropyCollector()
michael@0: :mBytesCollected(0), mWritePointer(mEntropyCache)
michael@0: {
michael@0:   // We could use the uninitialized memory in mEntropyCache as initial
michael@0:   // random data, but that means (if any entropy is collected before NSS
michael@0:   // initialization and then forwarded) that we'll get warnings from
michael@0:   // tools like valgrind for every later operation that depends on the
michael@0:   // entropy.
michael@0:   memset(mEntropyCache, 0, sizeof(mEntropyCache));
michael@0: }
michael@0: 
michael@0: nsEntropyCollector::~nsEntropyCollector()
michael@0: {
michael@0: }
michael@0: 
michael@0: NS_IMPL_ISUPPORTS(nsEntropyCollector,
michael@0:                   nsIEntropyCollector,
michael@0:                   nsIBufEntropyCollector)
michael@0: 
michael@0: NS_IMETHODIMP
michael@0: nsEntropyCollector::RandomUpdate(void *new_entropy, int32_t bufLen)
michael@0: {
michael@0:   if (bufLen > 0) {
michael@0:     if (mForwardTarget) {
michael@0:       return mForwardTarget->RandomUpdate(new_entropy, bufLen);
michael@0:     }
michael@0:     else {
michael@0:       const unsigned char *InputPointer = (const unsigned char *)new_entropy;
michael@0:       const unsigned char *PastEndPointer = mEntropyCache + entropy_buffer_size;
michael@0: 
michael@0:       // if the input is large, we only take as much as we can store
michael@0:       int32_t bytes_wanted = std::min(bufLen, int32_t(entropy_buffer_size));
michael@0: 
michael@0:       // remember the number of bytes we will have after storing new_entropy
michael@0:       mBytesCollected = std::min(int32_t(entropy_buffer_size),
michael@0:                                mBytesCollected + bytes_wanted);
michael@0: 
michael@0:       // as the above statements limit bytes_wanted to the entropy_buffer_size,
michael@0:       // this loop will iterate at most twice.
michael@0:       while (bytes_wanted > 0) {
michael@0: 
michael@0:         // how many bytes to end of cyclic buffer?
michael@0:         const int32_t space_to_end = PastEndPointer - mWritePointer;
michael@0: 
michael@0:         // how many bytes can we copy, not reaching the end of the buffer?
michael@0:         const int32_t this_time = std::min(space_to_end, bytes_wanted);
michael@0: 
michael@0:         // copy at most to the end of the cyclic buffer
michael@0:         for (int32_t i = 0; i < this_time; ++i) {
michael@0: 
michael@0:           unsigned int old = *mWritePointer;
michael@0: 
michael@0:           // combine new and old value already stored in buffer
michael@0:           // this logic comes from PSM 1
michael@0:           *mWritePointer++ = ((old << 1) | (old >> 7)) ^ *InputPointer++;
michael@0:         }
michael@0: 
michael@0:         PR_ASSERT(mWritePointer <= PastEndPointer);
michael@0:         PR_ASSERT(mWritePointer >= mEntropyCache);
michael@0: 
michael@0:         // have we arrived at the end of the buffer?
michael@0:         if (PastEndPointer == mWritePointer) {
michael@0:           // reset write pointer back to begining of our buffer
michael@0:           mWritePointer = mEntropyCache;
michael@0:         }
michael@0: 
michael@0:         // subtract the number of bytes we have already copied
michael@0:         bytes_wanted -= this_time;
michael@0:       }
michael@0:     }
michael@0:   }
michael@0: 
michael@0:   return NS_OK;
michael@0: }
michael@0: 
michael@0: NS_IMETHODIMP
michael@0: nsEntropyCollector::ForwardTo(nsIEntropyCollector *aCollector)
michael@0: {
michael@0:   NS_PRECONDITION(!mForwardTarget, "|ForwardTo| should only be called once.");
michael@0: 
michael@0:   mForwardTarget = aCollector;
michael@0:   mForwardTarget->RandomUpdate(mEntropyCache, mBytesCollected);
michael@0:   mBytesCollected = 0;
michael@0: 
michael@0:   return NS_OK;
michael@0: }
michael@0: 
michael@0: NS_IMETHODIMP
michael@0: nsEntropyCollector::DontForward()
michael@0: {
michael@0:   mForwardTarget = nullptr;
michael@0:   return NS_OK;
michael@0: }