#217 Compute acos with less cancellation near x=1

test/hypothesis/.gitignore

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+__pycache__
+.hypothesis
+.ipynb_checkpoints

test/hypothesis/error_hunt.py

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+from decimal import Decimal, getcontext
+import json
+import subprocess
+import hypothesis
+from hypothesis import given, settings
+from hypothesis.strategies import decimals, integers, tuples
+from mpmath import mp
+import pytest
+
+mp.prec = 500
+getcontext().prec = 14
+
+node = subprocess.Popen(
+    ["node", "evaluate.mjs"], stdout=subprocess.PIPE, stdin=subprocess.PIPE
+)
+
+
+def get_decimal(func: str, args: list, config: dict):
+    arg = json.dumps({"func": func, "args": args, "config": config}).encode() + b"\r"
+    node.stdin.write(arg)
+    node.stdin.flush()
+    return Decimal(node.stdout.readline().strip().decode())
+
+
+def assert_matches(x, mpfunc, jsfunc=None):
+    if jsfunc is None:
+        jsfunc = mpfunc
+    y = Decimal(str(getattr(mp, mpfunc)(x))) * Decimal("1.0")
+    z = get_decimal(jsfunc, [str(x)], {"precision": 14})
+    assert y == z
+
+
+@pytest.mark.parametrize("fn", "sin cos tan atan asinh".split())
+@given(
+    x=tuples(
+        decimals(
+            allow_nan=False, allow_infinity=False, min_value=-1, max_value=1, places=14
+        ),
+        integers(min_value=-99, max_value=99),
+    ).map(lambda tup: tup[0] * Decimal(10) ** tup[1])
+)
+@settings(max_examples=100_000)
+def test_matches(x, fn):
+    assert_matches(x, fn)
+
+
+@pytest.mark.parametrize("fn", "ln log10 sqrt".split())
+@given(
+    x=tuples(
+        decimals(
+            allow_nan=False,
+            allow_infinity=False,
+            min_value=1e-13,
+            max_value=1,
+            places=14,
+        ),
+        integers(min_value=-99, max_value=99),
+    ).map(lambda tup: tup[0] * Decimal(10) ** tup[1])
+)
+@settings(max_examples=100_000)
+def test_positive_domain(x, fn):
+    assert_matches(x, fn)
+
+
+@pytest.mark.parametrize("fn", "asin acos atanh".split())
+@given(
+    x=decimals(
+        allow_nan=False, allow_infinity=False, min_value=-1, max_value=1, places=14
+    )
+)
+@settings(max_examples=100_000)
+def test_inverse_trig(x, fn):
+    assert_matches(x, fn)
+
+
+@pytest.mark.parametrize("fn", "sinh cosh tanh exp".split())
+@given(
+    x=tuples(
+        decimals(
+            allow_nan=False, allow_infinity=False, min_value=-1, max_value=1, places=14
+        ),
+        integers(min_value=-99, max_value=3),
+    ).map(lambda tup: tup[0] * Decimal(10) ** tup[1])
+)
+@settings(max_examples=100_000)
+def test_small_domain(x, fn):
+    assert_matches(x, fn)
+
+@given(
+    x=tuples(
+        decimals(
+            allow_nan=False, allow_infinity=False, min_value=1, max_value=10, places=14
+        ),
+        integers(min_value=0, max_value=99),
+    ).map(lambda tup: tup[0] * Decimal(10) ** tup[1])
+)
+@settings(max_examples=100_000)
+def test_acosh(x):
+    assert_matches(x, 'acosh')

test/hypothesis/evaluate.mjs

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+// listen for test cases, and provide the results.
+// give JSON of the test case, receive the result
+// Example: 
+// > {"func":"tan", "args":["12.5"], "config":{"precision":8}}
+// -0.066468242
+
+
+import {Decimal} from '../../decimal.mjs';
+import {createInterface} from 'readline';
+
+const readline = createInterface({
+	input: process.stdin,
+	output: process.stdout
+});
+
+readline.on("close", () => {console.log('\n'); process.exit(0);});
+
+readline.on("line", (line) => {
+    if (line) {
+        const {func, args, config} = JSON.parse(line);
+        config.defaults = true;
+        Decimal.set(config);
+        const result = Decimal[func](...args);
+        console.log(result);
+    }
+});

test/hypothesis/requirements.txt

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+hypothesis
+mpmath
+node