f8d9fa9e80
This upgrades all of libgo other than the runtime package to the Go 1.4 release. In Go 1.4 much of the runtime was rewritten into Go. Merging that code will take more time and will not change the API, so I'm putting it off for now. There are a few runtime changes anyhow, to accomodate other packages that rely on minor modifications to the runtime support. The compiler changes slightly to add a one-bit flag to each type descriptor kind that is stored directly in an interface, which for gccgo is currently only pointer types. Another one-bit flag (gcprog) is reserved because it is used by the gc compiler, but gccgo does not currently use it. There is another error check in the compiler since I ran across it during testing. gotools/: * Makefile.am (go_cmd_go_files): Sort entries. Add generate.go. * Makefile.in: Rebuild. From-SVN: r219627
71 lines
1.7 KiB
Go
71 lines
1.7 KiB
Go
// Copyright 2012 The Go Authors. All rights reserved.
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// Use of this source code is governed by a BSD-style
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// license that can be found in the LICENSE file.
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package png
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// intSize is either 32 or 64.
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const intSize = 32 << (^uint(0) >> 63)
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func abs(x int) int {
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// m := -1 if x < 0. m := 0 otherwise.
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m := x >> (intSize - 1)
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// In two's complement representation, the negative number
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// of any number (except the smallest one) can be computed
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// by flipping all the bits and add 1. This is faster than
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// code with a branch.
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// See Hacker's Delight, section 2-4.
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return (x ^ m) - m
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}
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// paeth implements the Paeth filter function, as per the PNG specification.
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func paeth(a, b, c uint8) uint8 {
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// This is an optimized version of the sample code in the PNG spec.
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// For example, the sample code starts with:
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// p := int(a) + int(b) - int(c)
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// pa := abs(p - int(a))
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// but the optimized form uses fewer arithmetic operations:
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// pa := int(b) - int(c)
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// pa = abs(pa)
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pc := int(c)
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pa := int(b) - pc
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pb := int(a) - pc
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pc = abs(pa + pb)
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pa = abs(pa)
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pb = abs(pb)
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if pa <= pb && pa <= pc {
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return a
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} else if pb <= pc {
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return b
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}
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return c
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}
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// filterPaeth applies the Paeth filter to the cdat slice.
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// cdat is the current row's data, pdat is the previous row's data.
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func filterPaeth(cdat, pdat []byte, bytesPerPixel int) {
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var a, b, c, pa, pb, pc int
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for i := 0; i < bytesPerPixel; i++ {
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a, c = 0, 0
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for j := i; j < len(cdat); j += bytesPerPixel {
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b = int(pdat[j])
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pa = b - c
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pb = a - c
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pc = abs(pa + pb)
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pa = abs(pa)
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pb = abs(pb)
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if pa <= pb && pa <= pc {
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// No-op.
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} else if pb <= pc {
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a = b
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} else {
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a = c
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}
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a += int(cdat[j])
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a &= 0xff
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cdat[j] = uint8(a)
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c = b
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}
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}
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}
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