122 lines
3.1 KiB
Go
122 lines
3.1 KiB
Go
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// Copyright (c) 2012-2015 Ugorji Nwoke. All rights reserved.
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// Use of this source code is governed by a MIT license found in the LICENSE file.
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package codec
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// All non-std package dependencies live in this file,
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// so porting to different environment is easy (just update functions).
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func pruneSignExt(v []byte, pos bool) (n int) {
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if len(v) < 2 {
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} else if pos && v[0] == 0 {
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for ; v[n] == 0 && n+1 < len(v) && (v[n+1]&(1<<7) == 0); n++ {
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}
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} else if !pos && v[0] == 0xff {
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for ; v[n] == 0xff && n+1 < len(v) && (v[n+1]&(1<<7) != 0); n++ {
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}
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}
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return
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}
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// validate that this function is correct ...
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// culled from OGRE (Object-Oriented Graphics Rendering Engine)
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// function: halfToFloatI (http://stderr.org/doc/ogre-doc/api/OgreBitwise_8h-source.html)
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func halfFloatToFloatBits(yy uint16) (d uint32) {
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y := uint32(yy)
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s := (y >> 15) & 0x01
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e := (y >> 10) & 0x1f
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m := y & 0x03ff
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if e == 0 {
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if m == 0 { // plu or minus 0
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return s << 31
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}
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// Denormalized number -- renormalize it
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for (m & 0x00000400) == 0 {
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m <<= 1
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e -= 1
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}
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e += 1
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const zz uint32 = 0x0400
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m &= ^zz
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} else if e == 31 {
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if m == 0 { // Inf
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return (s << 31) | 0x7f800000
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}
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return (s << 31) | 0x7f800000 | (m << 13) // NaN
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}
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e = e + (127 - 15)
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m = m << 13
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return (s << 31) | (e << 23) | m
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}
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// GrowCap will return a new capacity for a slice, given the following:
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// - oldCap: current capacity
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// - unit: in-memory size of an element
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// - num: number of elements to add
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func growCap(oldCap, unit, num int) (newCap int) {
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// appendslice logic (if cap < 1024, *2, else *1.25):
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// leads to many copy calls, especially when copying bytes.
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// bytes.Buffer model (2*cap + n): much better for bytes.
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// smarter way is to take the byte-size of the appended element(type) into account
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// maintain 3 thresholds:
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// t1: if cap <= t1, newcap = 2x
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// t2: if cap <= t2, newcap = 1.75x
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// t3: if cap <= t3, newcap = 1.5x
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// else newcap = 1.25x
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//
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// t1, t2, t3 >= 1024 always.
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// i.e. if unit size >= 16, then always do 2x or 1.25x (ie t1, t2, t3 are all same)
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//
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// With this, appending for bytes increase by:
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// 100% up to 4K
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// 75% up to 8K
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// 50% up to 16K
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// 25% beyond that
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// unit can be 0 e.g. for struct{}{}; handle that appropriately
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var t1, t2, t3 int // thresholds
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if unit <= 1 {
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t1, t2, t3 = 4*1024, 8*1024, 16*1024
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} else if unit < 16 {
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t3 = 16 / unit * 1024
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t1 = t3 * 1 / 4
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t2 = t3 * 2 / 4
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} else {
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t1, t2, t3 = 1024, 1024, 1024
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}
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var x int // temporary variable
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// x is multiplier here: one of 5, 6, 7 or 8; incr of 25%, 50%, 75% or 100% respectively
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if oldCap <= t1 { // [0,t1]
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x = 8
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} else if oldCap > t3 { // (t3,infinity]
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x = 5
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} else if oldCap <= t2 { // (t1,t2]
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x = 7
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} else { // (t2,t3]
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x = 6
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}
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newCap = x * oldCap / 4
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if num > 0 {
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newCap += num
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}
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// ensure newCap is a multiple of 64 (if it is > 64) or 16.
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if newCap > 64 {
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if x = newCap % 64; x != 0 {
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x = newCap / 64
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newCap = 64 * (x + 1)
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}
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} else {
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if x = newCap % 16; x != 0 {
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x = newCap / 16
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newCap = 16 * (x + 1)
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}
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}
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return
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}
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