FAILURE MAP
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FA-61856 / Currency rounding and FX conversion / Open access

An unknown currency silently defaults to two minor digits · case 01

An unsupported code such as 'GBX' is formatted as if it were a cent currency.

Verified by executionVariant 1 · 7 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

The exponent lookup falls back to 2 instead of rejecting codes outside the table.

VERIFIED REPAIR

Return 'ERR:unknown-currency' for every normalized code missing from the exponent table.

Unsuccessful approach: Rejecting only codes whose length is not three still accepts well-formed but unsupported codes.

Case contract

solve(amount, ccy): amount is an exact decimal string, ccy an ISO-like code that is trimmed and upper-cased. Minor-unit exponents: USD 2, EUR 2, JPY 0, KRW 0, KWD 3, BHD 3, CLF 4. Round the exact decimal half-even at the currency exponent and return a plain string with exactly that many fraction digits; a zero result is unsigned. Unknown codes return 'ERR:unknown-currency'.

Why this case matters

Currency amounts must be rounded at the right stage and in the right unit, or ledgers, quotes and settlements drift by minor units.

1 / The failure

Exit 1
"""Failure Map reference implementation. Python standard library only."""
import json
from decimal import Decimal, ROUND_HALF_EVEN, ROUND_HALF_UP, ROUND_FLOOR, ROUND_CEILING, ROUND_DOWN, ROUND_UP, ROUND_HALF_DOWN
N = 1
observations = []
def solve(amount, ccy):
    exps = {'USD': 2, 'EUR': 2, 'JPY': 0, 'KRW': 0, 'KWD': 3, 'BHD': 3, 'CLF': 4}
    code = ccy.strip().upper()
    e = exps.get(code, 2)
    x = Decimal(amount)
    q = x.quantize(Decimal(1).scaleb(-e), rounding=ROUND_HALF_EVEN)
    if q == 0: q = abs(q)
    return format(q, 'f')
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
cases = [[('regression unknown-currency 1', ('1.005', 'GBX'), 'ERR:unknown-currency'),
  ('regression unknown-currency 2', ('1.0', 'ABCD'), 'ERR:unknown-currency'),
  ('partial repair guard 2', ('1.00', 'ABC'), 'ERR:unknown-currency'),
  ('control: cents tie to even', ('2.665', 'USD'), '2.66'), ('control: yen tie', ('1235.5', 'JPY'), '1236'),
  ('control: dinar three places', ('10.0005', 'KWD'), '10.000'),
  ('control: unit of account four places', ('1.23456', 'CLF'), '1.2346')],
 [('regression unknown-currency 1', ('1.00', 'ABC'), 'ERR:unknown-currency'),
  ('regression unknown-currency 2', ('15200.78697', 'GBX'), 'ERR:unknown-currency'),
  ('partial repair guard 2', ('47176.41', 'GBX'), 'ERR:unknown-currency'),
  ('control: unit of account four places', ('1.23456', 'CLF'), '1.2346'),
  ('control: lowercase code', ('12.345', ' eur '), '12.34'), ('control: negative small', ('-0.004', 'USD'), '0.00'),
  ('control: integer input', ('7', 'BHD'), '7.000')],
 [('regression unknown-currency 1', ('47176.41', 'GBX'), 'ERR:unknown-currency'),
  ('regression unknown-currency 2', ('24558.1895', 'GBX'), 'ERR:unknown-currency'),
  ('partial repair guard 2', ('20428.404', 'GBX'), 'ERR:unknown-currency'),
  ('control: integer input', ('7', 'BHD'), '7.000'), ('control: unknown code', ('1.00', 'ABC'), 'ERR:unknown-currency'),
  ('control: large amount', ('123456789.125', 'USD'), '123456789.12'),
  ('control: negative tie', ('-2.5', 'KRW'), '-2')],
 [('regression unknown-currency 1', ('20428.404', 'GBX'), 'ERR:unknown-currency'),
  ('regression unknown-currency 2', ('11999.89380', 'GBX'), 'ERR:unknown-currency'),
  ('partial repair guard 2', ('44143.650', 'GBX'), 'ERR:unknown-currency'),
  ('control: negative tie', ('-2.5', 'KRW'), '-2'), ('control: cents tie to even', ('2.665', 'USD'), '2.66'),
  ('control: yen tie', ('1235.5', 'JPY'), '1236'), ('control: dinar three places', ('10.0005', 'KWD'), '10.000')],
 [('regression unknown-currency 1', ('44143.650', 'GBX'), 'ERR:unknown-currency'),
  ('regression unknown-currency 2', ('34654.813830', 'GBX'), 'ERR:unknown-currency'),
  ('partial repair guard 2', ('17622.45', 'GBX'), 'ERR:unknown-currency'),
  ('control: dinar three places', ('10.0005', 'KWD'), '10.000'),
  ('control: unit of account four places', ('1.23456', 'CLF'), '1.2346'),
  ('control: lowercase code', ('12.345', ' eur '), '12.34'), ('control: negative small', ('-0.004', 'USD'), '0.00')]]
for label, args, expected in cases[N - 1]:
    check(label, solve(*args), expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)
Boundary fixtureActualExpectedOutcome
regression unknown-currency 11.00ERR:unknown-currencyFailed
regression unknown-currency 21.00ERR:unknown-currencyFailed
partial repair guard 21.00ERR:unknown-currencyFailed
control: cents tie to even2.662.66Passed
control: yen tie12361236Passed
control: dinar three places10.00010.000Passed
control: unit of account four places1.23461.2346Passed

SHA-256 / 26f1095f793ee67d0c42204c16adf27d72d066949f70100e7116827efd7ab3fb

2 / The unsuccessful fix

Exit 1
"""Failure Map reference implementation. Python standard library only."""
import json
from decimal import Decimal, ROUND_HALF_EVEN, ROUND_HALF_UP, ROUND_FLOOR, ROUND_CEILING, ROUND_DOWN, ROUND_UP, ROUND_HALF_DOWN
N = 1
observations = []
def solve(amount, ccy):
    exps = {'USD': 2, 'EUR': 2, 'JPY': 0, 'KRW': 0, 'KWD': 3, 'BHD': 3, 'CLF': 4}
    code = ccy.strip().upper()
    if code not in exps and len(code) != 3: return 'ERR:unknown-currency'
    e = exps.get(code, 2)
    x = Decimal(amount)
    q = x.quantize(Decimal(1).scaleb(-e), rounding=ROUND_HALF_EVEN)
    if q == 0: q = abs(q)
    return format(q, 'f')
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
cases = [[('regression unknown-currency 1', ('1.005', 'GBX'), 'ERR:unknown-currency'),
  ('regression unknown-currency 2', ('1.0', 'ABCD'), 'ERR:unknown-currency'),
  ('partial repair guard 2', ('1.00', 'ABC'), 'ERR:unknown-currency'),
  ('control: cents tie to even', ('2.665', 'USD'), '2.66'), ('control: yen tie', ('1235.5', 'JPY'), '1236'),
  ('control: dinar three places', ('10.0005', 'KWD'), '10.000'),
  ('control: unit of account four places', ('1.23456', 'CLF'), '1.2346')],
 [('regression unknown-currency 1', ('1.00', 'ABC'), 'ERR:unknown-currency'),
  ('regression unknown-currency 2', ('15200.78697', 'GBX'), 'ERR:unknown-currency'),
  ('partial repair guard 2', ('47176.41', 'GBX'), 'ERR:unknown-currency'),
  ('control: unit of account four places', ('1.23456', 'CLF'), '1.2346'),
  ('control: lowercase code', ('12.345', ' eur '), '12.34'), ('control: negative small', ('-0.004', 'USD'), '0.00'),
  ('control: integer input', ('7', 'BHD'), '7.000')],
 [('regression unknown-currency 1', ('47176.41', 'GBX'), 'ERR:unknown-currency'),
  ('regression unknown-currency 2', ('24558.1895', 'GBX'), 'ERR:unknown-currency'),
  ('partial repair guard 2', ('20428.404', 'GBX'), 'ERR:unknown-currency'),
  ('control: integer input', ('7', 'BHD'), '7.000'), ('control: unknown code', ('1.00', 'ABC'), 'ERR:unknown-currency'),
  ('control: large amount', ('123456789.125', 'USD'), '123456789.12'),
  ('control: negative tie', ('-2.5', 'KRW'), '-2')],
 [('regression unknown-currency 1', ('20428.404', 'GBX'), 'ERR:unknown-currency'),
  ('regression unknown-currency 2', ('11999.89380', 'GBX'), 'ERR:unknown-currency'),
  ('partial repair guard 2', ('44143.650', 'GBX'), 'ERR:unknown-currency'),
  ('control: negative tie', ('-2.5', 'KRW'), '-2'), ('control: cents tie to even', ('2.665', 'USD'), '2.66'),
  ('control: yen tie', ('1235.5', 'JPY'), '1236'), ('control: dinar three places', ('10.0005', 'KWD'), '10.000')],
 [('regression unknown-currency 1', ('44143.650', 'GBX'), 'ERR:unknown-currency'),
  ('regression unknown-currency 2', ('34654.813830', 'GBX'), 'ERR:unknown-currency'),
  ('partial repair guard 2', ('17622.45', 'GBX'), 'ERR:unknown-currency'),
  ('control: dinar three places', ('10.0005', 'KWD'), '10.000'),
  ('control: unit of account four places', ('1.23456', 'CLF'), '1.2346'),
  ('control: lowercase code', ('12.345', ' eur '), '12.34'), ('control: negative small', ('-0.004', 'USD'), '0.00')]]
for label, args, expected in cases[N - 1]:
    check(label, solve(*args), expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)
Boundary fixtureActualExpectedOutcome
regression unknown-currency 11.00ERR:unknown-currencyFailed
regression unknown-currency 2ERR:unknown-currencyERR:unknown-currencyPassed
partial repair guard 21.00ERR:unknown-currencyFailed
control: cents tie to even2.662.66Passed
control: yen tie12361236Passed
control: dinar three places10.00010.000Passed
control: unit of account four places1.23461.2346Passed

SHA-256 / f413fca2d9e95c7c52be5a209ffd607de6a1cde295e739f2eda23de8b107951e

3 / The verified repair

Exit 0
"""Failure Map reference implementation. Python standard library only."""
import json
from decimal import Decimal, ROUND_HALF_EVEN, ROUND_HALF_UP, ROUND_FLOOR, ROUND_CEILING, ROUND_DOWN, ROUND_UP, ROUND_HALF_DOWN
N = 1
observations = []
def solve(amount, ccy):
    exps = {'USD': 2, 'EUR': 2, 'JPY': 0, 'KRW': 0, 'KWD': 3, 'BHD': 3, 'CLF': 4}
    code = ccy.strip().upper()
    if code not in exps: return 'ERR:unknown-currency'
    e = exps[code]
    x = Decimal(amount)
    q = x.quantize(Decimal(1).scaleb(-e), rounding=ROUND_HALF_EVEN)
    if q == 0: q = abs(q)
    return format(q, 'f')
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
cases = [[('regression unknown-currency 1', ('1.005', 'GBX'), 'ERR:unknown-currency'),
  ('regression unknown-currency 2', ('1.0', 'ABCD'), 'ERR:unknown-currency'),
  ('partial repair guard 2', ('1.00', 'ABC'), 'ERR:unknown-currency'),
  ('control: cents tie to even', ('2.665', 'USD'), '2.66'), ('control: yen tie', ('1235.5', 'JPY'), '1236'),
  ('control: dinar three places', ('10.0005', 'KWD'), '10.000'),
  ('control: unit of account four places', ('1.23456', 'CLF'), '1.2346')],
 [('regression unknown-currency 1', ('1.00', 'ABC'), 'ERR:unknown-currency'),
  ('regression unknown-currency 2', ('15200.78697', 'GBX'), 'ERR:unknown-currency'),
  ('partial repair guard 2', ('47176.41', 'GBX'), 'ERR:unknown-currency'),
  ('control: unit of account four places', ('1.23456', 'CLF'), '1.2346'),
  ('control: lowercase code', ('12.345', ' eur '), '12.34'), ('control: negative small', ('-0.004', 'USD'), '0.00'),
  ('control: integer input', ('7', 'BHD'), '7.000')],
 [('regression unknown-currency 1', ('47176.41', 'GBX'), 'ERR:unknown-currency'),
  ('regression unknown-currency 2', ('24558.1895', 'GBX'), 'ERR:unknown-currency'),
  ('partial repair guard 2', ('20428.404', 'GBX'), 'ERR:unknown-currency'),
  ('control: integer input', ('7', 'BHD'), '7.000'), ('control: unknown code', ('1.00', 'ABC'), 'ERR:unknown-currency'),
  ('control: large amount', ('123456789.125', 'USD'), '123456789.12'),
  ('control: negative tie', ('-2.5', 'KRW'), '-2')],
 [('regression unknown-currency 1', ('20428.404', 'GBX'), 'ERR:unknown-currency'),
  ('regression unknown-currency 2', ('11999.89380', 'GBX'), 'ERR:unknown-currency'),
  ('partial repair guard 2', ('44143.650', 'GBX'), 'ERR:unknown-currency'),
  ('control: negative tie', ('-2.5', 'KRW'), '-2'), ('control: cents tie to even', ('2.665', 'USD'), '2.66'),
  ('control: yen tie', ('1235.5', 'JPY'), '1236'), ('control: dinar three places', ('10.0005', 'KWD'), '10.000')],
 [('regression unknown-currency 1', ('44143.650', 'GBX'), 'ERR:unknown-currency'),
  ('regression unknown-currency 2', ('34654.813830', 'GBX'), 'ERR:unknown-currency'),
  ('partial repair guard 2', ('17622.45', 'GBX'), 'ERR:unknown-currency'),
  ('control: dinar three places', ('10.0005', 'KWD'), '10.000'),
  ('control: unit of account four places', ('1.23456', 'CLF'), '1.2346'),
  ('control: lowercase code', ('12.345', ' eur '), '12.34'), ('control: negative small', ('-0.004', 'USD'), '0.00')]]
for label, args, expected in cases[N - 1]:
    check(label, solve(*args), expected)
print(json.dumps({"observations": observations, "passed": all(x["passed"] for x in observations)}, ensure_ascii=False))
raise SystemExit(0 if all(x["passed"] for x in observations) else 1)
Boundary fixtureActualExpectedOutcome
regression unknown-currency 1ERR:unknown-currencyERR:unknown-currencyPassed
regression unknown-currency 2ERR:unknown-currencyERR:unknown-currencyPassed
partial repair guard 2ERR:unknown-currencyERR:unknown-currencyPassed
control: cents tie to even2.662.66Passed
control: yen tie12361236Passed
control: dinar three places10.00010.000Passed
control: unit of account four places1.23461.2346Passed

SHA-256 / ca711d7c1fb2b58a25f6e9ec07634a3644d498c347dea29fb2b70f1a4c55eec0

Verification & scope

A deterministic, bounded teaching model with a stipulated toy contract; it makes no claim of conformance to any real regulation, standard, or institution's rules. This reproducer isolates one failure mechanism. Results cover the supplied fixtures. Variants within a family share a test contract and should remain grouped when constructing evaluation splits. Related mechanisms with a shared evaluation_group must also remain together; these controlled models are not independent production incidents.

Observations recorded using Python 3.12.14 at 2026-09-29T14:46:59.154655+00:00.

Case digest / e41cdc811fb090ceded782214a77c109b0634387865deae852b395ef1098ff31