use go 1.12

Signed-off-by: hongming <talonwan@yunify.com>

vendor/github.com/lucas-clemente/quic-go/internal/utils/float16.go

@@ -0,0 +1,86 @@
+package utils
+
+import (
+	"bytes"
+	"io"
+	"math"
+)
+
+// We define an unsigned 16-bit floating point value, inspired by IEEE floats
+// (http://en.wikipedia.org/wiki/Half_precision_floating-point_format),
+// with 5-bit exponent (bias 1), 11-bit mantissa (effective 12 with hidden
+// bit) and denormals, but without signs, transfinites or fractions. Wire format
+// 16 bits (little-endian byte order) are split into exponent (high 5) and
+// mantissa (low 11) and decoded as:
+//   uint64_t value;
+//   if (exponent == 0) value = mantissa;
+//   else value = (mantissa | 1 << 11) << (exponent - 1)
+const uFloat16ExponentBits = 5
+const uFloat16MaxExponent = (1 << uFloat16ExponentBits) - 2                                        // 30
+const uFloat16MantissaBits = 16 - uFloat16ExponentBits                                             // 11
+const uFloat16MantissaEffectiveBits = uFloat16MantissaBits + 1                                     // 12
+const uFloat16MaxValue = ((uint64(1) << uFloat16MantissaEffectiveBits) - 1) << uFloat16MaxExponent // 0x3FFC0000000
+
+// readUfloat16 reads a float in the QUIC-float16 format and returns its uint64 representation
+func readUfloat16(b io.ByteReader, byteOrder ByteOrder) (uint64, error) {
+	val, err := byteOrder.ReadUint16(b)
+	if err != nil {
+		return 0, err
+	}
+
+	res := uint64(val)
+
+	if res < (1 << uFloat16MantissaEffectiveBits) {
+		// Fast path: either the value is denormalized (no hidden bit), or
+		// normalized (hidden bit set, exponent offset by one) with exponent zero.
+		// Zero exponent offset by one sets the bit exactly where the hidden bit is.
+		// So in both cases the value encodes itself.
+		return res, nil
+	}
+
+	exponent := val >> uFloat16MantissaBits // No sign extend on uint!
+	// After the fast pass, the exponent is at least one (offset by one).
+	// Un-offset the exponent.
+	exponent--
+	// Here we need to clear the exponent and set the hidden bit. We have already
+	// decremented the exponent, so when we subtract it, it leaves behind the
+	// hidden bit.
+	res -= uint64(exponent) << uFloat16MantissaBits
+	res <<= exponent
+	return res, nil
+}
+
+// writeUfloat16 writes a float in the QUIC-float16 format from its uint64 representation
+func writeUfloat16(b *bytes.Buffer, byteOrder ByteOrder, value uint64) {
+	var result uint16
+	if value < (uint64(1) << uFloat16MantissaEffectiveBits) {
+		// Fast path: either the value is denormalized, or has exponent zero.
+		// Both cases are represented by the value itself.
+		result = uint16(value)
+	} else if value >= uFloat16MaxValue {
+		// Value is out of range; clamp it to the maximum representable.
+		result = math.MaxUint16
+	} 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.
+		exponent := uint16(0)
+		for offset := uint16(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 >= (uint64(1) << (uFloat16MantissaBits + offset)) {
+				exponent += offset
+				value >>= offset
+			}
+		}
+
+		// 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 = (uint16(value) + (exponent << uFloat16MantissaBits))
+	}
+
+	byteOrder.WriteUint16(b, result)
+}