Implemented new datasources (modbus,scpi)

internal/datasource/modbus/decode.go

@@ -0,0 +1,89 @@
+package modbus
+
+import (
+	"fmt"
+	"math"
+)
+
+// orderWords returns the registers in big-word-first order, reversing them when
+// the register declares little word order. The slice is copied so the caller's
+// data is left untouched.
+func (r Register) orderWords(words []uint16) []uint16 {
+	if !r.littleWordOrder() {
+		return words
+	}
+	out := make([]uint16, len(words))
+	for i, w := range words {
+		out[len(words)-1-i] = w
+	}
+	return out
+}
+
+// decode converts the raw registers into the register's numeric value and
+// applies scale/offset. The result type is int64 or float64 per dataType.
+func (r Register) decode(words []uint16) (any, error) {
+	w := r.orderWords(words)
+	var raw float64
+	var rawInt int64
+	switch r.encoding() {
+	case "uint16":
+		rawInt = int64(w[0])
+		raw = float64(w[0])
+	case "int16":
+		rawInt = int64(int16(w[0]))
+		raw = float64(int16(w[0]))
+	case "uint32":
+		u := uint32(w[0])<<16 | uint32(w[1])
+		rawInt = int64(u)
+		raw = float64(u)
+	case "int32":
+		u := uint32(w[0])<<16 | uint32(w[1])
+		rawInt = int64(int32(u))
+		raw = float64(int32(u))
+	case "float32":
+		u := uint32(w[0])<<16 | uint32(w[1])
+		raw = float64(math.Float32frombits(u))
+	case "float64":
+		u := uint64(w[0])<<48 | uint64(w[1])<<32 | uint64(w[2])<<16 | uint64(w[3])
+		raw = math.Float64frombits(u)
+	default:
+		return nil, fmt.Errorf("modbus: unknown encoding %q", r.Encoding)
+	}
+
+	// Integer fast-path: no scaling/offset, integer encoding.
+	if r.scale() == 1 && r.Offset == 0 {
+		switch r.encoding() {
+		case "uint16", "int16", "uint32", "int32":
+			return rawInt, nil
+		}
+	}
+	return raw*r.scale() + r.Offset, nil
+}
+
+// encode converts a value destined for a Write back into raw registers,
+// inverting scale/offset. Only the holding-register encodings are writable.
+func (r Register) encode(value float64) ([]uint16, error) {
+	v := (value - r.Offset) / r.scale()
+	var words []uint16
+	switch r.encoding() {
+	case "uint16":
+		words = []uint16{uint16(int64(math.Round(v)))}
+	case "int16":
+		words = []uint16{uint16(int16(int64(math.Round(v))))}
+	case "uint32":
+		u := uint32(int64(math.Round(v)))
+		words = []uint16{uint16(u >> 16), uint16(u)}
+	case "int32":
+		u := uint32(int32(int64(math.Round(v))))
+		words = []uint16{uint16(u >> 16), uint16(u)}
+	case "float32":
+		u := math.Float32bits(float32(v))
+		words = []uint16{uint16(u >> 16), uint16(u)}
+	case "float64":
+		u := math.Float64bits(v)
+		words = []uint16{uint16(u >> 48), uint16(u >> 32), uint16(u >> 16), uint16(u)}
+	default:
+		return nil, fmt.Errorf("modbus: unknown encoding %q", r.Encoding)
+	}
+	return r.orderWords(words), nil
+}