go-chart/seq/buffer.go

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package seq
import (
"fmt"
"strings"
2018-12-06 16:38:58 +01:00
util "git.gutmet.org/go-chart.git/util"
)
const (
bufferMinimumGrow = 4
bufferShrinkThreshold = 32
bufferGrowFactor = 200
bufferDefaultCapacity = 4
)
var (
emptyArray = make([]float64, 0)
)
// NewBuffer creates a new value buffer with an optional set of values.
func NewBuffer(values ...float64) *Buffer {
var tail int
array := make([]float64, util.Math.MaxInt(len(values), bufferDefaultCapacity))
if len(values) > 0 {
copy(array, values)
tail = len(values)
}
return &Buffer{
array: array,
head: 0,
tail: tail,
size: len(values),
}
}
// NewBufferWithCapacity creates a new ValueBuffer pre-allocated with the given capacity.
func NewBufferWithCapacity(capacity int) *Buffer {
return &Buffer{
array: make([]float64, capacity),
head: 0,
tail: 0,
size: 0,
}
}
// Buffer is a fifo datastructure that is backed by a pre-allocated array.
// Instead of allocating a whole new node object for each element, array elements are re-used (which saves GC churn).
// Enqueue can be O(n), Dequeue is generally O(1).
// Buffer implements `seq.Provider`
type Buffer struct {
array []float64
head int
tail int
size int
}
// Len returns the length of the Buffer (as it is currently populated).
// Actual memory footprint may be different.
func (b *Buffer) Len() int {
return b.size
}
// GetValue implements seq provider.
func (b *Buffer) GetValue(index int) float64 {
effectiveIndex := (b.head + index) % len(b.array)
return b.array[effectiveIndex]
}
// Capacity returns the total size of the Buffer, including empty elements.
func (b *Buffer) Capacity() int {
return len(b.array)
}
// SetCapacity sets the capacity of the Buffer.
func (b *Buffer) SetCapacity(capacity int) {
newArray := make([]float64, capacity)
if b.size > 0 {
if b.head < b.tail {
arrayCopy(b.array, b.head, newArray, 0, b.size)
} else {
arrayCopy(b.array, b.head, newArray, 0, len(b.array)-b.head)
arrayCopy(b.array, 0, newArray, len(b.array)-b.head, b.tail)
}
}
b.array = newArray
b.head = 0
if b.size == capacity {
b.tail = 0
} else {
b.tail = b.size
}
}
// Clear removes all objects from the Buffer.
func (b *Buffer) Clear() {
b.array = make([]float64, bufferDefaultCapacity)
b.head = 0
b.tail = 0
b.size = 0
}
// Enqueue adds an element to the "back" of the Buffer.
func (b *Buffer) Enqueue(value float64) {
if b.size == len(b.array) {
newCapacity := int(len(b.array) * int(bufferGrowFactor/100))
if newCapacity < (len(b.array) + bufferMinimumGrow) {
newCapacity = len(b.array) + bufferMinimumGrow
}
b.SetCapacity(newCapacity)
}
b.array[b.tail] = value
b.tail = (b.tail + 1) % len(b.array)
b.size++
}
// Dequeue removes the first element from the RingBuffer.
func (b *Buffer) Dequeue() float64 {
if b.size == 0 {
return 0
}
removed := b.array[b.head]
b.head = (b.head + 1) % len(b.array)
b.size--
return removed
}
// Peek returns but does not remove the first element.
func (b *Buffer) Peek() float64 {
if b.size == 0 {
return 0
}
return b.array[b.head]
}
// PeekBack returns but does not remove the last element.
func (b *Buffer) PeekBack() float64 {
if b.size == 0 {
return 0
}
if b.tail == 0 {
return b.array[len(b.array)-1]
}
return b.array[b.tail-1]
}
// TrimExcess resizes the capacity of the buffer to better fit the contents.
func (b *Buffer) TrimExcess() {
threshold := float64(len(b.array)) * 0.9
if b.size < int(threshold) {
b.SetCapacity(b.size)
}
}
// Array returns the ring buffer, in order, as an array.
func (b *Buffer) Array() Array {
newArray := make([]float64, b.size)
if b.size == 0 {
return newArray
}
if b.head < b.tail {
arrayCopy(b.array, b.head, newArray, 0, b.size)
} else {
arrayCopy(b.array, b.head, newArray, 0, len(b.array)-b.head)
arrayCopy(b.array, 0, newArray, len(b.array)-b.head, b.tail)
}
return Array(newArray)
}
// Each calls the consumer for each element in the buffer.
func (b *Buffer) Each(mapfn func(int, float64)) {
if b.size == 0 {
return
}
var index int
if b.head < b.tail {
for cursor := b.head; cursor < b.tail; cursor++ {
mapfn(index, b.array[cursor])
index++
}
} else {
for cursor := b.head; cursor < len(b.array); cursor++ {
mapfn(index, b.array[cursor])
index++
}
for cursor := 0; cursor < b.tail; cursor++ {
mapfn(index, b.array[cursor])
index++
}
}
}
// String returns a string representation for value buffers.
func (b *Buffer) String() string {
var values []string
for _, elem := range b.Array() {
values = append(values, fmt.Sprintf("%v", elem))
}
return strings.Join(values, " <= ")
}
// --------------------------------------------------------------------------------
// Util methods
// --------------------------------------------------------------------------------
func arrayClear(source []float64, index, length int) {
for x := 0; x < length; x++ {
absoluteIndex := x + index
source[absoluteIndex] = 0
}
}
func arrayCopy(source []float64, sourceIndex int, destination []float64, destinationIndex, length int) {
for x := 0; x < length; x++ {
from := sourceIndex + x
to := destinationIndex + x
destination[to] = source[from]
}
}