Abstract out segments mapping and use it in mmap storage

[btrtrc.git] / segments / segments.go

diff --git a/segments/segments.go b/segments/segments.go
new file mode 100644 (file)
index 0000000..97b611d
--- /dev/null
+++ b/segments/segments.go
@@ -0,0 +1,62 @@
+package segments
+
+type Int = int64
+
+type Length = Int
+
+func min(i Int, rest ...Int) Int {
+       ret := i
+       for _, i := range rest {
+               if i < ret {
+                       ret = i
+               }
+       }
+       return ret
+}
+
+type Extent struct {
+       Start, Length Int
+}
+
+func (e Extent) End() Int {
+       return e.Start + e.Length
+}
+
+type (
+       Callback   = func(int, Extent) bool
+       LengthIter = func() (Length, bool)
+)
+
+func Scan(haystack func() (Length, bool), needle Extent, callback Callback) {
+       i := 0
+       for needle.Length != 0 {
+               l, ok := haystack()
+               if !ok {
+                       return
+               }
+               if needle.Start < l || needle.Start == l && l == 0 {
+                       e1 := Extent{
+                               Start:  needle.Start,
+                               Length: min(l, needle.End()) - needle.Start,
+                       }
+                       if e1.Length >= 0 {
+                               if !callback(i, e1) {
+                                       return
+                               }
+                               needle.Start -= e1.Length
+                               needle.Length -= e1.Length
+                       }
+               } else {
+                       needle.Start -= l
+               }
+               i++
+       }
+}
+
+func LocaterFromLengthIter(li LengthIter) Locater {
+       return func(e Extent, c Callback) {
+               Scan(li, e, c)
+       }
+}
+
+type Locater func(Extent, Callback)