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Diffstat (limited to 'src/dotty/tools/dotc/core/pickling/TastyBuffer.scala')
-rw-r--r-- | src/dotty/tools/dotc/core/pickling/TastyBuffer.scala | 162 |
1 files changed, 162 insertions, 0 deletions
diff --git a/src/dotty/tools/dotc/core/pickling/TastyBuffer.scala b/src/dotty/tools/dotc/core/pickling/TastyBuffer.scala new file mode 100644 index 000000000..f6a7a17b4 --- /dev/null +++ b/src/dotty/tools/dotc/core/pickling/TastyBuffer.scala @@ -0,0 +1,162 @@ +package dotty.tools +package dotc +package core +package pickling + +import util.Util.dble + +object TastyBuffer { + + /** The number of digits of the natural number `nat`, written in base 128 format. */ + def natSize(nat: Int): Int = + if (nat < 128) 1 else natSize(nat >>> 7) + 1 + + /** An address pointing to an index in a Tasty buffer's byte array */ + class Addr(val index: Int) extends AnyVal { + def -(delta: Int): Addr = new Addr(this.index - delta) + def +(delta: Int): Addr = new Addr(this.index + delta) + + def relativeTo(base: Addr): Addr = this - base.index - AddrWidth + } + + /** The maximal number of address bytes. + * Since addresses are written as base-128 natural numbers, + * the value of 4 gives a maximal array size of 512M. + */ + final val AddrWidth = 4 +} +import TastyBuffer._ + +/** A byte array buffer that can be filled with bytes or natural numbers in TASTY format, + * and that supports reading and patching addresses represented as natural numbers. + */ +class TastyBuffer(initialSize: Int) { + + /** The current byte array, will be expanded as needed */ + var bytes = new Array[Byte](initialSize) + + /** The number of bytes written */ + var length = 0 + + // -- Output routines -------------------------------------------- + + /** Write a byte of data. */ + def writeByte(b: Int): Unit = { + if (length == bytes.length) bytes = dble(bytes) + bytes(length) = b.toByte + length += 1 + } + + /** Write the first `n` bytes of `data`. */ + def writeBytes(data: Array[Byte], n: Int): Unit = { + while (bytes.length < length + data.length) bytes = dble(bytes) + Array.copy(data, 0, bytes, length, n) + length += n + } + + /** Write a natural number in big endian format, base 128. + * All but the last digits have bit 0x80 set. + */ + def writeNat(x: Int): Unit = + writeLongNat(x.toLong & 0x00000000FFFFFFFFL) + + /** + * Like writeNat, but for longs. This is not the same as + * writeRaw, which writes in base 256. Note that the + * binary representation of LongNat is identical to Nat + * if the long value is in the range Int.MIN_VALUE to + * Int.MAX_VALUE. + */ + def writeLongNat(x: Long): Unit = { + def writeNatPrefix(x: Long): Unit = { + val y = x >>> 7 + if (y != 0L) writeNatPrefix(y) + writeByte(((x & 0x7f) | 0x80).toInt) + } + val y = x >>> 7 + if (y != 0L) writeNatPrefix(y) + writeByte((x & 0x7f).toInt) + } + + /** Write the `nbytes` least significant bytes of `x` in big endian format */ + def writeRaw(x: Long, nbytes: Int): Unit = { + def recur(x: Long, n: Int): Unit = + if (n > 0) { + recur(x >>> 8, n - 1) + writeByte((x & 0xff).toInt) + } + recur(x, nbytes) + } + + // -- Address handling -------------------------------------------- + + /** Write natural number `x` right-adjusted in a field of `width` bytes + * starting with address `at`. + */ + def putNat(at: Addr, x: Int, width: Int): Unit = { + var y = x + var w = width + var digit = y & 0x7f | 0x80 + while (w > 0) { + w -= 1 + bytes(at.index + w) = digit.toByte + y >>>= 7 + digit = y & 0x7f + } + assert(y == 0, s"number $x too large to fit in $width bytes") + } + + /** The byte at given address */ + def getByte(at: Addr): Int = bytes(at.index) + + /** The natural number at address `at` */ + def getNat(at: Addr): Int = getLongNat(at).toInt + + /** The long natural number at address `at` */ + def getLongNat(at: Addr): Long = { + var b = 0L + var x = 0L + var idx = at.index + do { + b = bytes(idx) + x = (x << 7) + (b & 0x7f) + idx += 1 + } while ((b & 0x80) != 0L) + x + } + + /** The address (represented as a natural number) at address `at` */ + def getAddr(at: Addr) = new Addr(getNat(at)) + + /** The smallest address equal to or following `at` which points to a non-zero byte */ + final def skipZeroes(at: Addr): Addr = + if (getByte(at) != 0) at else skipZeroes(at + 1) + + /** The address after the natural number found at address `at`. */ + final def skipNat(at: Addr): Addr = { + val next = at + 1 + if ((getByte(at) & 0x80) != 0) next else skipNat(next) + } + + /** The address referring to the end of data written so far */ + def currentAddr: Addr = new Addr(length) + + /** Reserve `AddrWidth` bytes to write an address into */ + def reserveAddr(): Addr = { + val result = currentAddr + length += AddrWidth + result + } + + /** Fill reserved space at address `at` with address `target` */ + def fillAddr(at: Addr, target: Addr) = + putNat(at, target.index, AddrWidth) + + // -- Finalization -------------------------------------------- + + /** Hook to be overridden in subclasses. + * Perform all actions necessary to assemble the final byte array. + * After `assemble` no more output actions to this buffer are permitted. + */ + def assemble(): Unit = () +} |