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contentenc: add PlainOffToCipherOff helper

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Will be used for improving Lseek()
This commit is contained in:
Jakob Unterwurzacher 2021-05-26 18:28:59 +02:00
parent b4794bedec
commit 07164cbb3a
2 changed files with 32 additions and 31 deletions
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16
internal/contentenc/offsets.go
View File

@ -76,20 +76,20 @@ func (be *ContentEnc) CipherSizeToPlainSize(cipherSize uint64) uint64 {
return cipherSize - overhead
}
// PlainSizeToCipherSize calculates the ciphertext size from a plaintext size
// PlainSizeToCipherSize calculates the ciphertext size from a plaintext size.
func (be *ContentEnc) PlainSizeToCipherSize(plainSize uint64) uint64 {
// Zero-sized files stay zero-sized
if plainSize == 0 {
return 0
}
return be.PlainOffToCipherOff(plainSize-1) + 1
}
// Block number at last byte
blockNo := be.PlainOffToBlockNo(plainSize - 1)
blockCount := blockNo + 1
overhead := be.BlockOverhead()*blockCount + HeaderLen
return plainSize + overhead
// PlainOffToCipherOff tells you the highest ciphertext offset that is
// *guaranteed* to be written/read when you write/read at `plainOff`.
func (be *ContentEnc) PlainOffToCipherOff(plainOff uint64) uint64 {
startOfBlock := be.BlockNoToCipherOff(be.PlainOffToBlockNo(plainOff))
return startOfBlock + plainOff%be.PlainBS() + be.BlockOverhead()
}
// ExplodePlainRange splits a plaintext byte range into (possibly partial) blocks

47
internal/contentenc/offsets_test.go
View File

@ -15,38 +15,39 @@ func TestSizeToSize(t *testing.T) {
const rangeMax = 10000
var c2p [rangeMax]uint64
var p2c [rangeMax]uint64
// y values in this order:
// 0 ... CipherSizeToPlainSize
// 1 ... PlainSizeToCipherSize
// 2 ... PlainOffToCipherOff
var yTable [rangeMax][3]uint64
// Calculate values
for i := range c2p {
c2p[i] = ce.CipherSizeToPlainSize(uint64(i))
p2c[i] = ce.PlainSizeToCipherSize(uint64(i))
for x := range yTable {
yTable[x][0] = ce.CipherSizeToPlainSize(uint64(x))
yTable[x][1] = ce.PlainSizeToCipherSize(uint64(x))
yTable[x][2] = ce.PlainOffToCipherOff(uint64(x))
}
// Print data table
fmt.Print("x\tToPlainSize\tToCipherSize\n")
for i := range c2p {
if i > 1 && i < rangeMax-1 {
fmt.Print("x\tCipherSizeToPlainSize\tPlainSizeToCipherSize\tPlainOffToCipherOff\n")
for x := range yTable {
if x > 1 && x < rangeMax-1 {
// If the point before has value-1 and the point after has value+1,
// it is not interesting. Don't print it out.
if c2p[i] == c2p[i-1]+1 && p2c[i] == p2c[i-1]+1 && c2p[i+1] == c2p[i]+1 && p2c[i+1] == p2c[i]+1 {
interesting := false
for i := 0; i <= 2; i++ {
if yTable[x-1][i]+1 != yTable[x][i] && yTable[x][i]+1 != yTable[x+1][i]+1 {
interesting = true
}
// Monotonicity check
if yTable[x][i] < yTable[x-1][i] {
t.Errorf("column %d is non-monotonic!", i)
}
}
if !interesting {
continue
}
}
fmt.Printf("%d\t%d\t%d\n", i, c2p[i], p2c[i])
}
// Monotonicity check
for i := range c2p {
if i < 1 {
continue
}
if c2p[i-1] > c2p[i] {
t.Errorf("error: c2p is non-monotonic: c2p[%d]=%d c2p[%d]=%d ", i-1, c2p[i-1], i, c2p[i])
}
if p2c[i-1] > p2c[i] {
t.Errorf("error: p2c is non-monotonic: p2c[%d]=%d p2c[%d]=%d ", i-1, p2c[i-1], i, p2c[i])
}
fmt.Printf("%d\t%d\t%d\t%d\n", x, yTable[x][0], yTable[x][1], yTable[x][2])
}
}