From 1fe7c47501699a5b29971b22fe6cbf8988e66b92 Mon Sep 17 00:00:00 2001
From: Samantha Abbott <52800387+sathabbott@users.noreply.github.com>
Date: Thu, 24 Sep 2026 17:07:42 +0000
Subject: [PATCH 1/2] Read a column's value range as IEEE 754 doubles

ColumnDescription.fMinValue / fMaxValue were read as little-endian int64
("<q"). The spec (Column Description) says the range is "specified as IEEE
754 little-endian double precision floats"; ROOT bit-casts a double through
a uint64 when serializing, which is presumably how the integer reading
crept in. Read them as "<d", typed float | None.

Reproduced on scikit-hep-testdata's test_float_types_rntuple_v1-0-0-0.root:
its seven Real32Quant columns (4 to 10) read as -4611686018427387904 /
4613937818241073152, the bit patterns of -2.0 / 3.0, and now read as the
doubles.

Also, from the same section of the spec:
- fFirstElementIndex is signed, as read: a negative value means the column
  is deferred and suppressed. Replace the TODO with that.
- Document field flag 0x08 (a collection stored in a SoA layout). It adds no
  optional field, so parsing is unchanged.

Fixes #75

Assisted-by: claude-code:claude-opus-5-5
---
 src/rootfilespec/rntuple/schema.py | 18 ++++++++++------
 tests/test_rntuple_schema.py       | 34 ++++++++++++++++++++++++++++++
 2 files changed, 45 insertions(+), 7 deletions(-)
 create mode 100644 tests/test_rntuple_schema.py

diff --git a/src/rootfilespec/rntuple/schema.py b/src/rootfilespec/rntuple/schema.py
index a25d326..e949d06 100644
--- a/src/rootfilespec/rntuple/schema.py
+++ b/src/rootfilespec/rntuple/schema.py
@@ -129,7 +129,9 @@ class FieldDescription(RecordFrame):
         - Bit:   Meaning
         - 0x01:  Repetitive field, i.e. for every entry `n` copies of the field are stored
         - 0x02:  Projected field
-        - 0x04:  Has ROOT type checksum as reported by TClass"""
+        - 0x04:  Has ROOT type checksum as reported by TClass
+        - 0x08:  The field is a collection that was stored using a SoA layout
+                 (no effect on the on-disk representation; adds no optional field)"""
     fFieldName: RString
     """The name of the field."""
     fTypeName: RString
@@ -178,13 +180,15 @@ class ColumnDescription(RecordFrame):
         - 0x02:  Column with a range of possible values"""
     fRepresentationIndex: Annotated[int, Fmt("<H")]
     """The index of the representation of the column in the list of representations for the field."""
-    # abbott TODO: verify the below are signed. make PR updating ROOT documentation if so (indicate signed bit in table)
     fFirstElementIndex: Annotated[int | None, OptionalField("<q", "fFlags", "&", 0x01)]
-    """The index of the first element in the column. Present only if flag 0x01 is set (deferred column)."""
-    fMinValue: Annotated[int | None, OptionalField("<q", "fFlags", "&", 0x02)]
-    """The minimum value of the column. Present only if flag 0x02 is set (column with range of values)."""
-    fMaxValue: Annotated[int | None, OptionalField("<q", "fFlags", "&", 0x02)]
-    """The maximum value of the column. Present only if flag 0x02 is set (column with range of values)."""
+    """The index of the first element in the column. Present only if flag 0x01 is set (deferred column).
+    Signed: a negative value means the column is deferred and suppressed."""
+    fMinValue: Annotated[float | None, OptionalField("<d", "fFlags", "&", 0x02)]
+    """The minimum value of the column, an IEEE 754 double.
+    Present only if flag 0x02 is set (column with range of values)."""
+    fMaxValue: Annotated[float | None, OptionalField("<d", "fFlags", "&", 0x02)]
+    """The maximum value of the column, an IEEE 754 double.
+    Present only if flag 0x02 is set (column with range of values)."""
 
 
 @serializable
diff --git a/tests/test_rntuple_schema.py b/tests/test_rntuple_schema.py
new file mode 100644
index 0000000..a1e1c23
--- /dev/null
+++ b/tests/test_rntuple_schema.py
@@ -0,0 +1,34 @@
+from skhep_testdata import data_path  # type: ignore[import-not-found]
+
+from rootfilespec.bootstrap import ROOT3a3aRNTuple
+from rootfilespec.reader import open_path
+from rootfilespec.rntuple.RNTuple import RNTuple
+from rootfilespec.rntuple.schema import ColumnType
+
+
+def test_column_value_range_is_double():
+    """Issue #75: a column's value range is a pair of IEEE 754 doubles
+
+    The file's quantized columns (4 to 10, fields quant1 to quant32) all have
+    the range [-2.0, 3.0]. Read as int64, the same bytes are the bit patterns
+    -4611686018427387904 and 4613937818241073152.
+    """
+    filename = "test_float_types_rntuple_v1-0-0-0.root"
+    with open_path(data_path(filename)) as reader:
+        anchor = reader.fetch(reader.keylist()["ntuple"])
+        assert isinstance(anchor, ROOT3a3aRNTuple)
+        rntuple = RNTuple.from_anchor(anchor, reader.fetch.buffer)
+
+    columns = rntuple.schemaDescription.columnDescriptions
+    with_range = [i for i, c in enumerate(columns) if c.fFlags & 0x02]
+    assert with_range == list(range(4, 11))
+    for i in with_range:
+        column = columns[i]
+        assert column.fColumnType == ColumnType.kReal32Quant
+        assert column.fMinValue == -2.0
+        assert column.fMaxValue == 3.0
+        assert isinstance(column.fMinValue, float)
+    for i, column in enumerate(columns):
+        if i not in with_range:
+            assert column.fMinValue is None
+            assert column.fMaxValue is None

From 1c0830a7ad02d023cb07c9192b8a2769f6a1f9d0 Mon Sep 17 00:00:00 2001
From: Samantha Abbott <52800387+sathabbott@users.noreply.github.com>
Date: Wed, 30 Sep 2026 14:17:31 +0000
Subject: [PATCH 2/2] Rename tests/test_rntuple_schema.py to
 tests/test_column_value_range.py

Name the module after what it tests, so it does not read as the home of a
broad set of tests (review on #125).

Assisted-by: claude-code:claude-opus-5-5
---
 tests/{test_rntuple_schema.py => test_column_value_range.py} | 0
 1 file changed, 0 insertions(+), 0 deletions(-)
 rename tests/{test_rntuple_schema.py => test_column_value_range.py} (100%)

diff --git a/tests/test_rntuple_schema.py b/tests/test_column_value_range.py
similarity index 100%
rename from tests/test_rntuple_schema.py
rename to tests/test_column_value_range.py