| // 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 |
| } |