Documentation
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Overview ¶
Package gcprog implements an encoder for packed GC pointer bitmaps, known as GC programs.
Program Format ¶
The GC program encodes a sequence of 0 and 1 bits indicating scalar or pointer words in an object. The encoding is a simple Lempel-Ziv program, with codes to emit literal bits and to repeat the last n bits c times.
The possible codes are:
00000000: stop 0nnnnnnn: emit n bits copied from the next (n+7)/8 bytes, least significant bit first 10000000 n c: repeat the previous n bits c times; n, c are varints 1nnnnnnn c: repeat the previous n bits c times; c is a varint
The numbers n and c, when they follow a code, are encoded as varints using the same encoding as encoding/binary's Uvarint.
Index ¶
- type Writer
- func (w *Writer) Append(prog []byte, n int64)
- func (w *Writer) BitIndex() int64
- func (w *Writer) Debug(out io.Writer)
- func (w *Writer) End()
- func (w *Writer) Init(writeByte func(byte))
- func (w *Writer) Ptr(index int64)
- func (w *Writer) Repeat(n, c int64)
- func (w *Writer) ShouldRepeat(n, c int64) bool
- func (w *Writer) ZeroUntil(index int64)
Constants ¶
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Variables ¶
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Functions ¶
This section is empty.
Types ¶
type Writer ¶
type Writer struct {
// contains filtered or unexported fields
}
A Writer is an encoder for GC programs.
The typical use of a Writer is to call Init, maybe call Debug, make a sequence of Ptr, Advance, Repeat, and Append calls to describe the data type, and then finally call End.
func (*Writer) Append ¶
Append emits the given GC program into the current output. The caller asserts that the program emits n bits (describes n words), and Append panics if that is not true.
func (*Writer) Debug ¶
Debug causes the writer to print a debugging trace to out during future calls to methods like Ptr, Advance, and End. It also enables debugging checks during the encoding.
func (*Writer) End ¶
func (w *Writer) End()
End marks the end of the program, writing any remaining bytes.
func (*Writer) Init ¶
Init initializes w to write a new GC program by calling writeByte for each byte in the program.
func (*Writer) Ptr ¶
Ptr emits a 1 into the bit stream at the given bit index. that is, it records that the index'th word in the object memory is a pointer. Any bits between the current index and the new index are set to zero, meaning the corresponding words are scalars.
func (*Writer) Repeat ¶
Repeat emits an instruction to repeat the description of the last n words c times (including the initial description, c+1 times in total).
func (*Writer) ShouldRepeat ¶
ShouldRepeat reports whether it would be worthwhile to use a Repeat to describe c elements of n bits each, compared to just emitting c copies of the n-bit description.
Source Files