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Diffstat (limited to 'vendor/github.com/golang/geo/s2/nthderivative.go')
| -rw-r--r-- | vendor/github.com/golang/geo/s2/nthderivative.go | 88 |
1 files changed, 0 insertions, 88 deletions
diff --git a/vendor/github.com/golang/geo/s2/nthderivative.go b/vendor/github.com/golang/geo/s2/nthderivative.go deleted file mode 100644 index 73445d6c9..000000000 --- a/vendor/github.com/golang/geo/s2/nthderivative.go +++ /dev/null @@ -1,88 +0,0 @@ -// Copyright 2017 Google Inc. All rights reserved. -// -// Licensed under the Apache License, Version 2.0 (the "License"); -// you may not use this file except in compliance with the License. -// You may obtain a copy of the License at -// -// http://www.apache.org/licenses/LICENSE-2.0 -// -// Unless required by applicable law or agreed to in writing, software -// distributed under the License is distributed on an "AS IS" BASIS, -// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. -// See the License for the specific language governing permissions and -// limitations under the License. - -package s2 - -// nthDerivativeCoder provides Nth Derivative Coding. -// (In signal processing disciplines, this is known as N-th Delta Coding.) -// -// Good for varint coding integer sequences with polynomial trends. -// -// Instead of coding a sequence of values directly, code its nth-order discrete -// derivative. Overflow in integer addition and subtraction makes this a -// lossless transform. -// -// constant linear quadratic -// trend trend trend -// / \ / \ / \_ -// input |0 0 0 0 1 2 3 4 9 16 25 36 -// 0th derivative(identity) |0 0 0 0 1 2 3 4 9 16 25 36 -// 1st derivative(delta coding) | 0 0 0 1 1 1 1 5 7 9 11 -// 2nd derivative(linear prediction) | 0 0 1 0 0 0 4 2 2 2 -// ------------------------------------- -// 0 1 2 3 4 5 6 7 8 9 10 11 -// n in sequence -// -// Higher-order codings can break even or be detrimental on other sequences. -// -// random oscillating -// / \ / \_ -// input |5 9 6 1 8 8 2 -2 4 -4 6 -6 -// 0th derivative(identity) |5 9 6 1 8 8 2 -2 4 -4 6 -6 -// 1st derivative(delta coding) | 4 -3 -5 7 0 -6 -4 6 -8 10 -12 -// 2nd derivative(linear prediction) | -7 -2 12 -7 -6 2 10 -14 18 -22 -// --------------------------------------- -// 0 1 2 3 4 5 6 7 8 9 10 11 -// n in sequence -// -// Note that the nth derivative isn't available until sequence item n. Earlier -// values are coded at lower order. For the above table, read 5 4 -7 -2 12 ... -type nthDerivativeCoder struct { - n, m int - memory [10]int32 -} - -// newNthDerivativeCoder returns a new coder, where n is the derivative order of the encoder (the N in NthDerivative). -// n must be within [0,10]. -func newNthDerivativeCoder(n int) *nthDerivativeCoder { - c := &nthDerivativeCoder{n: n} - if n < 0 || n > len(c.memory) { - panic("unsupported n. Must be within [0,10].") - } - return c -} - -func (c *nthDerivativeCoder) encode(k int32) int32 { - for i := 0; i < c.m; i++ { - delta := k - c.memory[i] - c.memory[i] = k - k = delta - } - if c.m < c.n { - c.memory[c.m] = k - c.m++ - } - return k -} - -func (c *nthDerivativeCoder) decode(k int32) int32 { - if c.m < c.n { - c.m++ - } - for i := c.m - 1; i >= 0; i-- { - c.memory[i] += k - k = c.memory[i] - } - return k -} |