104 lines
2.8 KiB
Markdown
104 lines
2.8 KiB
Markdown
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# returns
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Demonstrates working with function return values.
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## Multiple Unnamed Return Values
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Use `ReturnIndex` to reference unnamed return values. For example, the following function returns `start, start + size`.
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[embedmd]:# (asm.go go /.*TEXT.*Interval/ /RET.*/)
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```go
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TEXT("Interval", "func(start, size uint64) (uint64, uint64)")
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Doc(
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"Interval returns the (start, end) of an interval with the given start and size.",
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"Demonstrates multiple unnamed return values.",
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)
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start := Load(Param("start"), GP64v())
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size := Load(Param("size"), GP64v())
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end := size
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ADDQ(start, end)
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Store(start, ReturnIndex(0))
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Store(end, ReturnIndex(1))
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RET()
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```
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## Multiple Named Return Values
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Named return values are referenced much the same as arguments. For example, the following computes `(x0+x1, x0-x1)`.
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[embedmd]:# (asm.go go /.*TEXT.*Butterfly/ /RET.*/)
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```go
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TEXT("Butterfly", "func(x0, x1 float64) (y0, y1 float64)")
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Doc(
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"Butterfly performs a 2-dimensional butterfly operation: computes (x0+x1, x0-x1).",
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"Demonstrates multiple named return values.",
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)
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x0 := Load(Param("x0"), Xv())
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x1 := Load(Param("x1"), Xv())
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y0, y1 := Xv(), Xv()
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MOVSD(x0, y0)
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ADDSD(x1, y0)
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MOVSD(x0, y1)
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SUBSD(x1, y1)
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Store(y0, Return("y0"))
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Store(y1, Return("y1"))
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RET()
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```
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## Returning Data Structures
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Again just like function arguments, sub-components of return values can be referenced. This enables you to return data structures from your assembly functions.
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The following code returns an array type.
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[embedmd]:# (asm.go go /.*TEXT.*Septuple/ /RET.*/)
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```go
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TEXT("Septuple", "func(byte) [7]byte")
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Doc(
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"Septuple returns an array of seven of the given byte.",
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"Demonstrates returning array values.",
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)
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b := Load(ParamIndex(0), GP8v())
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for i := 0; i < 7; i++ {
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Store(b, ReturnIndex(0).Index(i))
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}
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RET()
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```
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Or a complex type:
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[embedmd]:# (asm.go go /.*TEXT.*CriticalLine/ /RET.*/)
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```go
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TEXT("CriticalLine", "func(t float64) complex128")
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Doc(
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"CriticalLine returns the complex value 0.5 + it on Riemann's critical line.",
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"Demonstrates returning complex values.",
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)
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t := Load(Param("t"), Xv())
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half := Xv()
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MOVSD(ConstData("half", F64(0.5)), half)
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Store(half, ReturnIndex(0).Real())
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Store(t, ReturnIndex(0).Imag())
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RET()
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```
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You can even build a struct:
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[embedmd]:# (asm.go go /.*TEXT.*NewStruct/ /RET.*/)
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```go
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TEXT("NewStruct", "func(w uint16, p [2]float64, q uint64) Struct")
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Doc(
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"NewStruct initializes a Struct value.",
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"Demonstrates returning struct values.",
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)
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w := Load(Param("w"), GP16v())
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x := Load(Param("p").Index(0), Xv())
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y := Load(Param("p").Index(1), Xv())
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q := Load(Param("q"), GP64v())
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Store(w, ReturnIndex(0).Field("Word"))
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Store(x, ReturnIndex(0).Field("Point").Index(0))
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Store(y, ReturnIndex(0).Field("Point").Index(1))
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Store(q, ReturnIndex(0).Field("Quad"))
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RET()
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```
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