mirror of
https://github.com/tinygo-org/tinygo.git
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Ayke van Laethem
88b6b2e7f5
TODO: do better at it by tracking min/max values of integers. The
following straightforward code doesn't have its bounds checks removed:
for _, n := range slice {
println(n)
}
61 lines
2.4 KiB
Go
61 lines
2.4 KiB
Go
package runtime
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// This file implements Go interfaces.
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//
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// Interfaces are represented as a pair of {typecode, value}, where value can be
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// anything (including non-pointers).
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//
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// Signatures itself are not matched on strings, but on uniqued numbers that
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// contain the name and the signature of the function (to save space), think of
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// signatures as interned strings at compile time.
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//
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// The typecode is a small number unique for the Go type. All typecodes <
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// firstInterfaceNum do not have any methods and typecodes >= firstInterfaceNum
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// all have at least one method. This means that methodSetRanges does not need
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// to contain types without methods and is thus indexed starting at a typecode
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// with number firstInterfaceNum.
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//
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// To further conserve some space, the methodSetRange (as the name indicates)
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// doesn't contain a list of methods and function pointers directly, but instead
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// just indexes into methodSetSignatures and methodSetFunctions which contains
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// the mapping from uniqued signature to function pointer.
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type _interface struct {
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typecode uint16
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value *uint8
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}
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// This struct indicates the range of methods in the methodSetSignatures and
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// methodSetFunctions arrays that belong to this named type.
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type methodSetRange struct {
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index uint16 // start index into interfaceSignatures and interfaceFunctions
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length uint16 // number of methods
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}
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// Global constants that will be set by the compiler. The arrays are of size 0,
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// which is a dummy value, but will be bigger after the compiler has filled them
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// in.
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var (
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firstInterfaceNum uint16 // the lowest typecode that has at least one method
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methodSetRanges [0]methodSetRange // indexes into methodSetSignatures and methodSetFunctions
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methodSetSignatures [0]uint16 // uniqued method ID
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methodSetFunctions [0]*uint8 // function pointer of method
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)
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// Get the function pointer for the method on the interface.
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// This is a compiler intrinsic.
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//go:nobounds
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func interfaceMethod(itf _interface, method uint16) *uint8 {
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// This function doesn't do bounds checking as the supplied method must be
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// in the list of signatures. The compiler will only emit
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// runtime.interfaceMethod calls when the method actually exists on this
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// interface (proven by the typechecker).
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i := methodSetRanges[itf.typecode-firstInterfaceNum].index
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for {
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if methodSetSignatures[i] == method {
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return methodSetFunctions[i]
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}
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i++
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}
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}
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