jit(arm64): various float instructions (#257)

Signed-off-by: Takeshi Yoneda <takeshi@tetrate.io>

internal/moremath/moremath.go

@@ -1,4 +1,4 @@
-package internal
+package moremath
 
 import "math"
 
@@ -44,3 +44,47 @@ func WasmCompatMax(x, y float64) float64 {
 	}
 	return y
 }
+
+// WasmCompatNearestF32 is the Wasm spec compatible variant of math.Round, which is used for Nearest instruction.
+// For example, this converts 1.9 to 2.0, and this has the semantics of LLVM's rint instrinsic: https://llvm.org/docs/LangRef.html#llvm-rint-intrinsic.
+// For the difference from math.Round, math.Round(-4.5) results in -5 while this produces -4.
+func WasmCompatNearestF32(f float32) float32 {
+	// TODO: look at https://github.com/bytecodealliance/wasmtime/pull/2171 and reconsider this algorithm
+	if f != -0 && f != 0 {
+		ceil := float32(math.Ceil(float64(f)))
+		floor := float32(math.Floor(float64(f)))
+		distToCeil := math.Abs(float64(f - ceil))
+		distToFloor := math.Abs(float64(f - floor))
+		h := ceil / 2.0
+		if distToCeil < distToFloor {
+			f = ceil
+		} else if distToCeil == distToFloor && float32(math.Floor(float64(h))) == h {
+			f = ceil
+		} else {
+			f = floor
+		}
+	}
+	return f
+}
+
+// WasmCompatNearestF64 is the Wasm spec compatible variant of math.Round, which is used for Nearest instruction.
+// For example, this converts 1.9 to 2.0, and this has the semantics of LLVM's rint instrinsic: https://llvm.org/docs/LangRef.html#llvm-rint-intrinsic.
+// For the difference from math.Round, math.Round(-4.5) results in -5 while this produces -4.
+func WasmCompatNearestF64(f float64) float64 {
+	// TODO: look at https://github.com/bytecodealliance/wasmtime/pull/2171 and reconsider this algorithm
+	if f != -0 && f != 0 {
+		ceil := math.Ceil(f)
+		floor := math.Floor(f)
+		distToCeil := math.Abs(f - ceil)
+		distToFloor := math.Abs(f - floor)
+		h := ceil / 2.0
+		if distToCeil < distToFloor {
+			f = ceil
+		} else if distToCeil == distToFloor && math.Floor(float64(h)) == h {
+			f = ceil
+		} else {
+			f = floor
+		}
+	}
+	return f
+}