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Diffstat (limited to 'vendor/github.com/klauspost/compress/compressible.go')
-rw-r--r-- | vendor/github.com/klauspost/compress/compressible.go | 85 |
1 files changed, 0 insertions, 85 deletions
diff --git a/vendor/github.com/klauspost/compress/compressible.go b/vendor/github.com/klauspost/compress/compressible.go deleted file mode 100644 index ea5a692d5..000000000 --- a/vendor/github.com/klauspost/compress/compressible.go +++ /dev/null @@ -1,85 +0,0 @@ -package compress - -import "math" - -// Estimate returns a normalized compressibility estimate of block b. -// Values close to zero are likely uncompressible. -// Values above 0.1 are likely to be compressible. -// Values above 0.5 are very compressible. -// Very small lengths will return 0. -func Estimate(b []byte) float64 { - if len(b) < 16 { - return 0 - } - - // Correctly predicted order 1 - hits := 0 - lastMatch := false - var o1 [256]byte - var hist [256]int - c1 := byte(0) - for _, c := range b { - if c == o1[c1] { - // We only count a hit if there was two correct predictions in a row. - if lastMatch { - hits++ - } - lastMatch = true - } else { - lastMatch = false - } - o1[c1] = c - c1 = c - hist[c]++ - } - - // Use x^0.6 to give better spread - prediction := math.Pow(float64(hits)/float64(len(b)), 0.6) - - // Calculate histogram distribution - variance := float64(0) - avg := float64(len(b)) / 256 - - for _, v := range hist { - Δ := float64(v) - avg - variance += Δ * Δ - } - - stddev := math.Sqrt(float64(variance)) / float64(len(b)) - exp := math.Sqrt(1 / float64(len(b))) - - // Subtract expected stddev - stddev -= exp - if stddev < 0 { - stddev = 0 - } - stddev *= 1 + exp - - // Use x^0.4 to give better spread - entropy := math.Pow(stddev, 0.4) - - // 50/50 weight between prediction and histogram distribution - return math.Pow((prediction+entropy)/2, 0.9) -} - -// ShannonEntropyBits returns the number of bits minimum required to represent -// an entropy encoding of the input bytes. -// https://en.wiktionary.org/wiki/Shannon_entropy -func ShannonEntropyBits(b []byte) int { - if len(b) == 0 { - return 0 - } - var hist [256]int - for _, c := range b { - hist[c]++ - } - shannon := float64(0) - invTotal := 1.0 / float64(len(b)) - for _, v := range hist[:] { - if v > 0 { - n := float64(v) - shannon += math.Ceil(-math.Log2(n*invTotal) * n) - } - } - return int(math.Ceil(shannon)) -} |