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