diff --git a/.jules/bolt.md b/.jules/bolt.md new file mode 100644 index 00000000..b5a840fe --- /dev/null +++ b/.jules/bolt.md @@ -0,0 +1,9 @@ +# Bolt's Journal + +## 2024-05-22 - [Buffer Allocation in Hot Loops] +**Learning:** In Go, repeatedly allocating buffers inside a loop (especially in I/O intensive code) generates significant GC pressure. +**Action:** Use `sync.Pool` or pre-allocate buffers outside the loop when possible. + +## 2024-05-22 - [Reflection in Binary Reading] +**Learning:** `binary.Read` uses reflection which is slow for simple types in hot paths. +**Action:** Use `io.ReadFull` with a byte slice and `binary.LittleEndian.UintXX` (or BigEndian) for primitive types in performance-critical sections. diff --git a/pkg/dicomio/reader.go b/pkg/dicomio/reader.go index dd64c2a2..3cf48be0 100644 --- a/pkg/dicomio/reader.go +++ b/pkg/dicomio/reader.go @@ -35,6 +35,9 @@ type Reader struct { // particular encoding.Decoder within this CodingSystem is nil, assume // UTF-8. cs charset.CodingSystem + // scratch is a buffer used for small reads to avoid allocating new slices + // for every read operation (which binary.Read would otherwise do via reflection). + scratch [8]byte } // NewReader creates and returns a new *dicomio.Reader. @@ -77,51 +80,58 @@ func (r *Reader) Read(p []byte) (int, error) { // ReadUInt8 reads an uint8 from the underlying *Reader. func (r *Reader) ReadUInt8() (uint8, error) { - var out uint8 - err := binary.Read(r, r.bo, &out) - return out, err + if _, err := io.ReadFull(r, r.scratch[:1]); err != nil { + return 0, err + } + return r.scratch[0], nil } // ReadUInt16 reads an uint16 from the underlying *Reader. func (r *Reader) ReadUInt16() (uint16, error) { - var out uint16 - err := binary.Read(r, r.bo, &out) - return out, err + if _, err := io.ReadFull(r, r.scratch[:2]); err != nil { + return 0, err + } + return r.bo.Uint16(r.scratch[:2]), nil } // ReadUInt32 reads an uint32 from the underlying *Reader. func (r *Reader) ReadUInt32() (uint32, error) { - var out uint32 - err := binary.Read(r, r.bo, &out) - return out, err + if _, err := io.ReadFull(r, r.scratch[:4]); err != nil { + return 0, err + } + return r.bo.Uint32(r.scratch[:4]), nil } // ReadInt16 reads an int16 from the underlying *Reader. func (r *Reader) ReadInt16() (int16, error) { - var out int16 - err := binary.Read(r, r.bo, &out) - return out, err + if _, err := io.ReadFull(r, r.scratch[:2]); err != nil { + return 0, err + } + return int16(r.bo.Uint16(r.scratch[:2])), nil } // ReadInt32 reads an int32 from the underlying *Reader. func (r *Reader) ReadInt32() (int32, error) { - var out int32 - err := binary.Read(r, r.bo, &out) - return out, err + if _, err := io.ReadFull(r, r.scratch[:4]); err != nil { + return 0, err + } + return int32(r.bo.Uint32(r.scratch[:4])), nil } // ReadFloat32 reads a float32 from the underlying *Reader. func (r *Reader) ReadFloat32() (float32, error) { - var out float32 - err := binary.Read(r, r.bo, &out) - return out, err + if _, err := io.ReadFull(r, r.scratch[:4]); err != nil { + return 0, err + } + return math.Float32frombits(r.bo.Uint32(r.scratch[:4])), nil } // ReadFloat64 reads a float64 from the underlying *Reader. func (r *Reader) ReadFloat64() (float64, error) { - var out float64 - err := binary.Read(r, r.bo, &out) - return out, err + if _, err := io.ReadFull(r, r.scratch[:8]); err != nil { + return 0, err + } + return math.Float64frombits(r.bo.Uint64(r.scratch[:8])), nil } func internalReadString(data []byte, d *encoding.Decoder) (string, error) {