bits: Add from_f32le, to_f32le, ...

TODO:
- show somehow generalize to/from encodings?
- move code to somwewhere else?

Author: wader

format/bits/bits.go

@@ -2,14 +2,21 @@ package bits
 
 import (
 	"embed"
+	"encoding/binary"
+	"fmt"
+	"math"
 
 	"github.com/wader/fq/format"
+	"github.com/wader/fq/internal/gojqex"
+	"github.com/wader/fq/internal/mathex"
+	"github.com/wader/fq/pkg/bitio"
 	"github.com/wader/fq/pkg/decode"
 	"github.com/wader/fq/pkg/interp"
 	"github.com/wader/fq/pkg/scalar"
 )
 
 //go:embed bits.md
+//go:embed bits.jq
 //go:embed bytes.md
 var bitsFS embed.FS
 
@@ -39,5 +46,74 @@ func init() {
 			DecodeFn:           decodeBits(8),
 			SkipDecodeFunction: true, // skip add bytes and frombytes function
 		})
+	interp.RegisterFunc2("_from_float", func(_ *interp.Interp, c any, nBits int, isLE bool) any {
+		switch nBits {
+		case 16, 32, 64:
+		default:
+			return fmt.Errorf("unsupported bit size %d, must be 16, 32 or 64", nBits)
+		}
+
+		br, err := interp.ToBitReader(c)
+		if err != nil {
+			return err
+		}
+		var b [8]byte
+		bs := b[:][0 : nBits/8]
+		_, err = br.ReadBits(bs[:], int64(nBits))
+		if err != nil {
+			return err
+		}
+		if isLE {
+			decode.ReverseBytes(bs[:])
+		}
+
+		switch nBits {
+		case 64:
+			return math.Float64frombits(binary.BigEndian.Uint64(bs[:]))
+		case 32:
+			return float64(math.Float32frombits(binary.BigEndian.Uint32(bs[:])))
+		case 16:
+			return float64(mathex.Float16(binary.BigEndian.Uint16(bs[:])).Float32())
+		default:
+			panic("unreachable")
+		}
+	})
+	interp.RegisterFunc2("_to_float", func(_ *interp.Interp, c any, nBits int, isLE bool) any {
+		switch nBits {
+		case 16, 32, 64:
+		default:
+			return fmt.Errorf("unsupported bit size %d, must be 16, 32 or 64", nBits)
+		}
+
+		v, ok := gojqex.Cast[float64](c)
+		if !ok {
+			return gojqex.FuncTypeError{Name: "_to_float", V: v}
+		}
+
+		var b [8]byte
+		bs := b[:][0 : nBits/8]
+		switch nBits {
+		case 64:
+			binary.BigEndian.PutUint64(bs, math.Float64bits(v))
+		case 32:
+			binary.BigEndian.PutUint32(bs, math.Float32bits(float32(v)))
+		case 16:
+			binary.BigEndian.PutUint16(bs, uint16(mathex.NewFloat16(float32(v))))
+		default:
+			panic("unreachable")
+		}
+		if isLE {
+			decode.ReverseBytes(bs[:])
+		}
+
+		br, err := interp.NewBinaryFromBitReader(bitio.NewBitReader(bs, -1), 8, 0)
+		if err != nil {
+			return err
+		}
+
+		return br
+
+	})
+
 	interp.RegisterFS(bitsFS)
 }

format/bits/bits.jq

@@ -0,0 +1,12 @@
+def from_f16be: _from_float(16; false);
+def from_f32be: _from_float(32; false);
+def from_f64be: _from_float(64; false);
+def from_f16le: _from_float(16; true);
+def from_f32le: _from_float(32; true);
+def from_f64le: _from_float(64; true);
+def to_f16le: _to_float(16; true);
+def to_f32le: _to_float(32; true);
+def to_f64le: _to_float(64; true);
+def to_f16be: _to_float(16; false);
+def to_f32be: _to_float(32; false);
+def to_f64be: _to_float(64; false);