Land Recent QUIC changes.

net/quic/quic_data_writer.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "net/quic/quic_data_writer.h"
 
 #include <algorithm>
 #include <limits>
 #include <string>
 
@@ skipping 38 matching lines @@
 bool QuicDataWriter::WriteUInt48(uint64 value) {
   uint32 hi = value >> 32;
   uint32 lo = value & GG_UINT64_C(0x00000000FFFFFFFF);
   return WriteUInt32(lo) && WriteUInt16(hi);
 }
 
 bool QuicDataWriter::WriteUInt64(uint64 value) {
   return WriteBytes(&value, sizeof(value));
 }
 
+bool QuicDataWriter::WriteUFloat16(uint64 value) {
+  uint16 result;
+  if (value < (GG_UINT64_C(1) << kUFloat16MantissaEffectiveBits)) {
+    // Fast path: either the value is denormalized, or has exponent zero.
+    // Both cases are represented by the value itself.
+    result = value;
+  } else if (value >= kUFloat16MaxValue) {
+    // Value is out of range; clamp it to the maximum representable.
+    result = numeric_limits<uint16>::max();
+  } else {
+    // The highest bit is between position 13 and 42 (zero-based), which
+    // corresponds to exponent 1-30. In the output, mantissa is from 0 to 10,
+    // hidden bit is 11 and exponent is 11 to 15. Shift the highest bit to 11
+    // and count the shifts.
+    uint16 exponent = 0;
+    for (uint16 offset = 16; offset > 0; offset /= 2) {
+      // Right-shift the value until the highest bit is in position 11.
+      // For offset of 16, 8, 4, 2 and 1 (binary search over 1-30),
+      // shift if the bit is at or above 11 + offset.
+      if (value >= (GG_UINT64_C(1) << (kUFloat16MantissaBits + offset))) {
+        exponent += offset;
+        value >>= offset;
+      }
+    }
+
+    DCHECK_GE(exponent, 1);
+    DCHECK_LE(exponent, kUFloat16MaxExponent);
+    DCHECK_GE(value, GG_UINT64_C(1) << kUFloat16MantissaBits);
+    DCHECK_LT(value, GG_UINT64_C(1) << kUFloat16MantissaEffectiveBits);
+
+    // Hidden bit (position 11) is set. We should remove it and increment the
+    // exponent. Equivalently, we just add it to the exponent.
+    // This hides the bit.
+    result = value + (exponent << kUFloat16MantissaBits);
+  }
+
+  return WriteBytes(&result, sizeof(result));
+}
+
 bool QuicDataWriter::WriteStringPiece16(StringPiece val) {
   if (val.length() > numeric_limits<uint16>::max()) {
     return false;
   }
   if (!WriteUInt16(val.size())) {
     return false;
   }
   return WriteBytes(val.data(), val.size());
 }
 
@@ skipping 70 matching lines @@
   DCHECK_LT(offset, capacity_);
   size_t latched_length = length_;
   length_ = offset;
   bool success = WriteUInt48(value);
   DCHECK_LE(length_, latched_length);
   length_ = latched_length;
   return success;
 }
 
 }  // namespace net