FA-84616 / Betting odds conversion / Open access

Off-ladder prices silently snapped · case 01

A 2.01 request is treated as a valid tick.

Verified by executionVariant 1 · 8 checks per implementationDownload source bundle ↓JSON ↗

ROOT CAUSE

The within-band remainder is never checked.

THE FAILURE

The within-band remainder is never checked.

Unsuccessful approach: Rounding to the nearest tick index still accepts invalid prices.

Case contract

Signed tick distance from price a to price b on the ladder [(101, 200, 1), (200, 300, 2), (300, 400, 5), (400, 600, 10), (600, 1000, 20), (1000, 2000, 50), (2000, 3000, 100), (3000, 5000, 200), (5000, 10000, 500), (10000, 100001, 1000)] (hundredths). Prices must be within 1.01..1000 ("invalid") and exactly on a tick ("off ladder"). Tick index counts all ticks of lower bands ((hi - lo) / step each) plus (v - lo) / step within the band. Return index(b) - index(a).

Why this case matters

Trading bots express stop-loss and offset orders as tick counts across ladder bands.

1 / The failure

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json
from fractions import Fraction
N = 1
observations = []
def solve(a, b):
    BANDS = [(101, 200, 1), (200, 300, 2), (300, 400, 5), (400, 600, 10), (600, 1000, 20), (1000, 2000, 50), (2000, 3000, 100), (3000, 5000, 200), (5000, 10000, 500), (10000, 100001, 1000)]
    def index(v):
        n = 0
        for lo, hi, step in BANDS:
            if v >= hi:
                n += (hi - lo) // step
            else:
                return n + (v - lo) // step
        return None
    out = []
    for p in (a, b):
        c = Fraction(p) * 100
        if c.denominator != 1 or c < 101 or c > 100000:
            return 'invalid'
        i = index(int(c))
        if i is None:
            return 'off ladder'
        out.append(i)
    return out[1] - out[0]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
def run(args):
    try:
        return solve(*args)
    except Exception as exc:
        return 'raised ' + type(exc).__name__
cases = [[('control within band', ('1.50', '1.60'), 10),
  ('boundary crossing two', ('1.98', '2.04'), 4),
  ('control downward move', ('3.10', '2.90'), -7),
  ('boundary off ladder', ('2.01', '2.50'), 'off ladder'),
  ('control full ladder', ('1.01', '1000'), 349),
  ('regression: off ladder detection', ('2.01', '5.50'), 'off ladder'),
  ('variant scenario 1', ('29.00', '10.00'), -29),
  ('variant scenario 2', ('12.00', '160.00'), 52)],
 [('control within band', ('1.50', '1.60'), 10),
  ('boundary crossing two', ('1.98', '2.04'), 4),
  ('control downward move', ('3.10', '2.90'), -7),
  ('boundary off ladder', ('2.01', '2.50'), 'off ladder'),
  ('control full ladder', ('1.01', '1000'), 349),
  ('regression: off ladder detection', ('55.00', '11.01'), 'off ladder'),
  ('variant scenario 1', ('2.18', '2.72'), 27),
  ('variant scenario 2', ('190.00', '3.20'), -115)],
 [('control within band', ('1.50', '1.60'), 10),
  ('boundary crossing two', ('1.98', '2.04'), 4),
  ('control downward move', ('3.10', '2.90'), -7),
  ('boundary off ladder', ('2.01', '2.50'), 'off ladder'),
  ('control full ladder', ('1.01', '1000'), 349),
  ('regression: off ladder detection', ('5.51', '1.61'), 'off ladder'),
  ('variant scenario 1', ('1.57', '13.00'), 159),
  ('variant scenario 2', ('2.84', '3.50'), 18)],
 [('control within band', ('1.50', '1.60'), 10),
  ('boundary crossing two', ('1.98', '2.04'), 4),
  ('control downward move', ('3.10', '2.90'), -7),
  ('boundary off ladder', ('2.01', '2.50'), 'off ladder'),
  ('control full ladder', ('1.01', '1000'), 349),
  ('regression: off ladder detection', ('4.41', '4.00'), 'off ladder'),
  ('variant scenario 1', ('6.20', '13.00'), 25),
  ('variant scenario 2', ('80.00', '15.50'), -35)],
 [('control within band', ('1.50', '1.60'), 10),
  ('boundary crossing two', ('1.98', '2.04'), 4),
  ('control downward move', ('3.10', '2.90'), -7),
  ('boundary off ladder', ('2.01', '2.50'), 'off ladder'),
  ('control full ladder', ('1.01', '1000'), 349),
  ('regression: off ladder detection', ('5.91', '20.00'), 'off ladder'),
  ('variant scenario 1', ('16.50', '1.41'), -182),
  ('variant scenario 2', ('10.00', '2.32'), -94)]]
for label, args, expected in cases[N - 1]:
    check(label, run(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 fixture	Actual	Expected	Outcome
control within band	`10`	`10`	Passed
boundary crossing two	`4`	`4`	Passed
control downward move	`-7`	`-7`	Passed
boundary off ladder	`25`	`off ladder`	Failed
control full ladder	`349`	`349`	Passed
regression: off ladder detection	`85`	`off ladder`	Failed
variant scenario 1	`-29`	`-29`	Passed
variant scenario 2	`52`	`52`	Passed

SHA-256 / 09f990f2140586e406657c0102dae059455a578c97f5b304feafc7651f43a0c1

2 / The unsuccessful fix

Exit 1

"""Failure Map reference implementation. Python standard library only."""
import json
from fractions import Fraction
N = 1
observations = []
def solve(a, b):
    BANDS = [(101, 200, 1), (200, 300, 2), (300, 400, 5), (400, 600, 10), (600, 1000, 20), (1000, 2000, 50), (2000, 3000, 100), (3000, 5000, 200), (5000, 10000, 500), (10000, 100001, 1000)]
    def index(v):
        n = 0
        for lo, hi, step in BANDS:
            if v >= hi:
                n += (hi - lo) // step
            else:
                return n + round((v - lo) / step)
        return None
    out = []
    for p in (a, b):
        c = Fraction(p) * 100
        if c.denominator != 1 or c < 101 or c > 100000:
            return 'invalid'
        i = index(int(c))
        if i is None:
            return 'off ladder'
        out.append(i)
    return out[1] - out[0]
def check(label, actual, expected):
    observations.append({"check": label, "actual": actual, "expected": expected, "passed": actual == expected})
def run(args):
    try:
        return solve(*args)
    except Exception as exc:
        return 'raised ' + type(exc).__name__
cases = [[('control within band', ('1.50', '1.60'), 10),
  ('boundary crossing two', ('1.98', '2.04'), 4),
  ('control downward move', ('3.10', '2.90'), -7),
  ('boundary off ladder', ('2.01', '2.50'), 'off ladder'),
  ('control full ladder', ('1.01', '1000'), 349),
  ('regression: off ladder detection', ('2.01', '5.50'), 'off ladder'),
  ('variant scenario 1', ('29.00', '10.00'), -29),
  ('variant scenario 2', ('12.00', '160.00'), 52)],
 [('control within band', ('1.50', '1.60'), 10),
  ('boundary crossing two', ('1.98', '2.04'), 4),
  ('control downward move', ('3.10', '2.90'), -7),
  ('boundary off ladder', ('2.01', '2.50'), 'off ladder'),
  ('control full ladder', ('1.01', '1000'), 349),
  ('regression: off ladder detection', ('55.00', '11.01'), 'off ladder'),
  ('variant scenario 1', ('2.18', '2.72'), 27),
  ('variant scenario 2', ('190.00', '3.20'), -115)],
 [('control within band', ('1.50', '1.60'), 10),
  ('boundary crossing two', ('1.98', '2.04'), 4),
  ('control downward move', ('3.10', '2.90'), -7),
  ('boundary off ladder', ('2.01', '2.50'), 'off ladder'),
  ('control full ladder', ('1.01', '1000'), 349),
  ('regression: off ladder detection', ('5.51', '1.61'), 'off ladder'),
  ('variant scenario 1', ('1.57', '13.00'), 159),
  ('variant scenario 2', ('2.84', '3.50'), 18)],
 [('control within band', ('1.50', '1.60'), 10),
  ('boundary crossing two', ('1.98', '2.04'), 4),
  ('control downward move', ('3.10', '2.90'), -7),
  ('boundary off ladder', ('2.01', '2.50'), 'off ladder'),
  ('control full ladder', ('1.01', '1000'), 349),
  ('regression: off ladder detection', ('4.41', '4.00'), 'off ladder'),
  ('variant scenario 1', ('6.20', '13.00'), 25),
  ('variant scenario 2', ('80.00', '15.50'), -35)],
 [('control within band', ('1.50', '1.60'), 10),
  ('boundary crossing two', ('1.98', '2.04'), 4),
  ('control downward move', ('3.10', '2.90'), -7),
  ('boundary off ladder', ('2.01', '2.50'), 'off ladder'),
  ('control full ladder', ('1.01', '1000'), 349),
  ('regression: off ladder detection', ('5.91', '20.00'), 'off ladder'),
  ('variant scenario 1', ('16.50', '1.41'), -182),
  ('variant scenario 2', ('10.00', '2.32'), -94)]]
for label, args, expected in cases[N - 1]:
    check(label, run(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 fixture	Actual	Expected	Outcome
control within band	`10`	`10`	Passed
boundary crossing two	`4`	`4`	Passed
control downward move	`-7`	`-7`	Passed
boundary off ladder	`25`	`off ladder`	Failed
control full ladder	`349`	`349`	Passed
regression: off ladder detection	`85`	`off ladder`	Failed
variant scenario 1	`-29`	`-29`	Passed
variant scenario 2	`52`	`52`	Passed

SHA-256 / ec5573e14fe26b32ebb627a8d2d48f5c8b092a3c6070f3014e69dcd27468dc70

HELD IN THE MEMBER ARCHIVE

The verified repair and its recorded checks are member-only.

This mechanism has 8 recorded checks per implementation. The open-access tier publishes the failure and the unsuccessful fix; the repaired source that passes every check, and the observations that prove it, are available to members.

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Verification & scope

Stipulated, bounded toy contract stated in the contract field; not a claim of conformance with any operator, exchange or regulator rule set. 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 2026-09-29T14:50:32.594443+00:00.

Case digest / bd33ebeb826bb5d4026c41a85dec4636cf552ade871e5d3e2c0d22ba30d4be9d