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8cdced3850
This is not a verbatim implementation of the Gorilla encoding. First of all, it could not, even if we wanted, because Prometheus has a different chunking model (constant size, not constant time). Second, this adds a number of changes that improve the encoding in general or at least for the specific use case of Prometheus (and are partially only possible in the context of Prometheus). See comments in the code for details.
76 lines
2.3 KiB
Go
76 lines
2.3 KiB
Go
// Copyright 2016 The Prometheus Authors
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// Licensed under the Apache License, Version 2.0 (the "License");
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// you may not use this file except in compliance with the License.
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// You may obtain a copy of the License at
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//
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// http://www.apache.org/licenses/LICENSE-2.0
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//
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// Unless required by applicable law or agreed to in writing, software
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// distributed under the License is distributed on an "AS IS" BASIS,
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// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
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// See the License for the specific language governing permissions and
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// limitations under the License.
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package local
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import "github.com/prometheus/common/model"
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var (
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// bit masks for consecutive bits in a byte at various offsets.
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bitMask = [][]byte{
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{0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00}, // 0 bit
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{0x80, 0x40, 0x20, 0x10, 0x08, 0x04, 0x02, 0x01}, // 1 bit
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{0xC0, 0x60, 0x30, 0x18, 0x0C, 0x06, 0x03, 0x01}, // 2 bit
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{0xE0, 0x70, 0x38, 0x1C, 0x0E, 0x07, 0x03, 0x01}, // 3 bit
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{0xF0, 0x78, 0x3C, 0x1E, 0x0F, 0x07, 0x03, 0x01}, // 4 bit
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{0xF8, 0x7C, 0x3E, 0x1F, 0x0F, 0x07, 0x03, 0x01}, // 5 bit
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{0xFC, 0x7E, 0x3F, 0x1F, 0x0F, 0x07, 0x03, 0x01}, // 6 bit
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{0xFE, 0x7F, 0x3F, 0x1F, 0x0F, 0x07, 0x03, 0x01}, // 7 bit
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{0xFF, 0x7F, 0x3F, 0x1F, 0x0F, 0x07, 0x03, 0x01}, // 8 bit
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}
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)
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// isInt32 returns true if v can be represented as an int32.
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func isInt32(v model.SampleValue) bool {
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return model.SampleValue(int32(v)) == v
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}
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// countBits returs the number of leading zero bits and the number of
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// significant bits after that in the given bit pattern. The maximum number of
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// leading zeros is 31 (so that it can be represented by a 5bit number). Leading
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// zeros beyond that are considered part of the significant bits.
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func countBits(pattern uint64) (leading, significant byte) {
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// TODO(beorn7): This would probably be faster with ugly endless switch
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// statements.
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if pattern == 0 {
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return
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}
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for pattern < 1<<63 {
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leading++
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pattern <<= 1
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}
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for pattern > 0 {
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significant++
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pattern <<= 1
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}
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if leading > 31 { // 5 bit limit.
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significant += leading - 31
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leading = 31
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}
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return
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}
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// isSignedIntN returns if n can be represented as a signed int with the given
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// bit length.
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func isSignedIntN(i int64, n byte) bool {
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upper := int64(1) << (n - 1)
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if i >= upper {
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return false
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}
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lower := upper - (1 << n)
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if i < lower {
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return false
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}
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return true
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}
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