Phase 6.a: DECIMAL/MONEY row decoding works (COUNT/SUM/AVG return Decimal)
Before:
cur.execute('SELECT COUNT(*) FROM systables')
cur.fetchone() # → (b'\xc2\x02\x00\x00\x00\x00\x00\x00\x00',) raw bytes
After:
cur.execute('SELECT COUNT(*) FROM systables')
cur.fetchone() # → (Decimal('276'),)
The trickiest decode of the project so far. IDS DECIMAL/MONEY wire format:
byte[0] = (sign << 7) | biased_exponent_base100
bit 7 = sign (1=positive, 0=negative)
bits 0-6 = (exponent + 64), XOR'd with 0x7F if negative
byte[1..] = digit-pair bytes (each 0..99 = two BCD digits)
if negative: asymmetric base-100 complement applied:
walk digits right→left, trailing zeros stay zero,
first non-zero subtracts from 100, rest from 99
Initial naive "99 - d for all digits" decoder gave artifacts like
-1234.559999 instead of -1234.56. The asymmetric complement rule
(from Decimal.decComplement line 447) is what makes negatives
round-trip exactly.
Width on the wire: per-column encoded_length packed as
(precision << 8) | scale; byte width = ceil(precision/2) + 1.
parse_tuple_payload uses this to slice DECIMAL columns correctly.
Tested cases all decode correctly:
COUNT(*) → Decimal('276')
SUM(tabid) → Decimal('55')
AVG(tabid) → Decimal('5.5')
1234.56::DECIMAL → Decimal('1234.56')
-1234.56::DECIMAL → Decimal('-1234.56')
-0.5::DECIMAL → Decimal('-0.5')
-99.99::DECIMAL → Decimal('-99.99')
-12345678.9::DECIMAL → Decimal('-12345678.9')
NULL → None
Encoder (_encode_decimal) is implemented but disabled — server rejects
the produced bytes (precision packing not quite right). Phase 6.x will
fix. Workaround: cast Decimal to float, or pass via SQL literal.
Module changes:
src/informix_db/converters.py:
+ decimal module import
+ _decode_decimal — full BCD decoder with asymmetric complement
+ _encode_decimal (Phase 6.x stub — present but unreached)
+ DECIMAL/MONEY added to DECODERS dispatch
src/informix_db/_resultset.py:
+ DECIMAL/MONEY width computation from encoded_length
Tests: 40 unit + 55 integration (8 new DECIMAL) = 95 total, all
green, ruff clean.
Ryan Malloy
2bacbc4e53