Initial commit

vendor/github.com/HdrHistogram/hdrhistogram-go/zigzag.go

@@ -0,0 +1,133 @@
+package hdrhistogram
+
+import "fmt"
+
+const truncatedErrStr = "Truncated compressed histogram decode. Expected minimum length of %d bytes and got %d."
+
+// Read an LEB128 ZigZag encoded long value from the given buffer
+func zig_zag_decode_i64(buf []byte) (signedValue int64, n int, err error) {
+	buflen := len(buf)
+	if buflen < 1 {
+		return 0, 0, nil
+	}
+	var value = uint64(buf[0]) & 0x7f
+	n = 1
+	if (buf[0] & 0x80) != 0 {
+		if buflen < 2 {
+			err = fmt.Errorf(truncatedErrStr, 2, buflen)
+			return
+		}
+		value |= uint64(buf[1]) & 0x7f << 7
+		n = 2
+		if (buf[1] & 0x80) != 0 {
+			if buflen < 3 {
+				err = fmt.Errorf(truncatedErrStr, 3, buflen)
+				return
+			}
+			value |= uint64(buf[2]) & 0x7f << 14
+			n = 3
+			if (buf[2] & 0x80) != 0 {
+				if buflen < 4 {
+					err = fmt.Errorf(truncatedErrStr, 4, buflen)
+					return
+				}
+				value |= uint64(buf[3]) & 0x7f << 21
+				n = 4
+				if (buf[3] & 0x80) != 0 {
+					if buflen < 5 {
+						err = fmt.Errorf(truncatedErrStr, 5, buflen)
+						return
+					}
+					value |= uint64(buf[4]) & 0x7f << 28
+					n = 5
+					if (buf[4] & 0x80) != 0 {
+						if buflen < 6 {
+							err = fmt.Errorf(truncatedErrStr, 6, buflen)
+							return
+						}
+						value |= uint64(buf[5]) & 0x7f << 35
+						n = 6
+						if (buf[5] & 0x80) != 0 {
+							if buflen < 7 {
+								err = fmt.Errorf(truncatedErrStr, 7, buflen)
+								return
+							}
+							value |= uint64(buf[6]) & 0x7f << 42
+							n = 7
+							if (buf[6] & 0x80) != 0 {
+								if buflen < 8 {
+									err = fmt.Errorf(truncatedErrStr, 8, buflen)
+									return
+								}
+								value |= uint64(buf[7]) & 0x7f << 49
+								n = 8
+								if (buf[7] & 0x80) != 0 {
+									if buflen < 9 {
+										err = fmt.Errorf(truncatedErrStr, 9, buflen)
+										return
+									}
+									value |= uint64(buf[8]) << 56
+									n = 9
+								}
+							}
+						}
+					}
+				}
+			}
+		}
+	}
+	signedValue = int64((value >> 1) ^ -(value & 1))
+	return
+}
+
+// Writes a int64_t value to the given buffer in LEB128 ZigZag encoded format
+// ZigZag encoding maps signed integers to unsigned integers so that numbers with a small
+// absolute value (for instance, -1) have a small varint encoded value too.
+// It does this in a way that "zig-zags" back and forth through the positive and negative integers,
+// so that -1 is encoded as 1, 1 is encoded as 2, -2 is encoded as 3, and so on.
+func zig_zag_encode_i64(signedValue int64) (buffer []byte) {
+	buffer = make([]byte, 0)
+	var value = uint64((signedValue << 1) ^ (signedValue >> 63))
+	if value>>7 == 0 {
+		buffer = append(buffer, byte(value))
+	} else {
+		buffer = append(buffer, byte((value&0x7F)|0x80))
+		if value>>14 == 0 {
+			buffer = append(buffer, byte(value>>7))
+		} else {
+			buffer = append(buffer, byte((value>>7)|0x80))
+			if value>>21 == 0 {
+				buffer = append(buffer, byte(value>>14))
+			} else {
+				buffer = append(buffer, byte((value>>14)|0x80))
+				if value>>28 == 0 {
+					buffer = append(buffer, byte(value>>21))
+				} else {
+					buffer = append(buffer, byte((value>>21)|0x80))
+					if value>>35 == 0 {
+						buffer = append(buffer, byte(value>>28))
+					} else {
+						buffer = append(buffer, byte((value>>28)|0x80))
+						if value>>42 == 0 {
+							buffer = append(buffer, byte(value>>35))
+						} else {
+							buffer = append(buffer, byte((value>>35)|0x80))
+							if value>>49 == 0 {
+								buffer = append(buffer, byte(value>>42))
+							} else {
+								buffer = append(buffer, byte((value>>42)|0x80))
+								if value>>56 == 0 {
+									buffer = append(buffer, byte(value>>49))
+								} else {
+									buffer = append(buffer, byte((value>>49)|0x80))
+									buffer = append(buffer, byte(value>>56))
+								}
+							}
+						}
+					}
+				}
+			}
+		}
+	}
+	return
+}