c8742e2b96
These variants uses an unsafe.Pointer instead of uintptr so that the pointer/non-pointer fields match those of real slices and strings. This may be necessary in the future once we switch to a precise garbage collector.
60 строки
1,8 КиБ
Go
60 строки
1,8 КиБ
Go
package reflect
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import (
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"unsafe"
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)
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// This stores a varint for each named type. Named types are identified by their
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// name instead of by their type. The named types stored in this struct are
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// non-basic types: pointer, struct, and channel.
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//go:extern reflect.namedNonBasicTypesSidetable
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var namedNonBasicTypesSidetable uintptr
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//go:extern reflect.structTypesSidetable
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var structTypesSidetable byte
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//go:extern reflect.structNamesSidetable
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var structNamesSidetable byte
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//go:extern reflect.arrayTypesSidetable
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var arrayTypesSidetable byte
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// readStringSidetable reads a string from the given table (like
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// structNamesSidetable) and returns this string. No heap allocation is
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// necessary because it makes the string point directly to the raw bytes of the
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// table.
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func readStringSidetable(table unsafe.Pointer, index uintptr) string {
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nameLen, namePtr := readVarint(unsafe.Pointer(uintptr(table) + index))
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return *(*string)(unsafe.Pointer(&stringHeader{
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data: namePtr,
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len: nameLen,
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}))
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}
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// readVarint decodes a varint as used in the encoding/binary package.
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// It has an input pointer and returns the read varint and the pointer
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// incremented to the next field in the data structure, just after the varint.
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//
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// Details:
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// https://github.com/golang/go/blob/e37a1b1c/src/encoding/binary/varint.go#L7-L25
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func readVarint(buf unsafe.Pointer) (uintptr, unsafe.Pointer) {
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var n uintptr
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shift := uintptr(0)
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for {
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// Read the next byte in the buffer.
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c := *(*byte)(buf)
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// Decode the bits from this byte and add them to the output number.
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n |= uintptr(c&0x7f) << shift
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shift += 7
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// Increment the buf pointer (pointer arithmetic!).
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buf = unsafe.Pointer(uintptr(buf) + 1)
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// Check whether this is the last byte of this varint. The upper bit
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// (msb) indicates whether any bytes follow.
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if c>>7 == 0 {
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return n, buf
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}
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}
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}
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