Remove duplicate nthRoot tests and add tightest Half* boundary cases

Author: Pablo1Gustavo

tests/BigDecimalTest.php

@@ -3244,6 +3244,18 @@ public static function providerNthRoot(): Generator
             ['-17', 3, 0, RoundingMode::Down,        '-2'],
             ['-17', 3, 0, RoundingMode::Up,          '-3'],
             ['-17', 3, 0, RoundingMode::HalfUp,      '-3'],
+
+            // Tightest possible Half* boundaries, where 2^n·|V| differs from (2·|t|+1)^n by ±1.
+            // V=43, n=3: 2^3·43 = 344 vs 7^3 = 343 (diff +1) → smallest "round up". ∛43 ≈ 3.5034.
+            ['43',  3, 0, RoundingMode::Unnecessary, 'NTH_ROOT_NOT_EXACT'],
+            ['43',  3, 0, RoundingMode::Down,        '3'],
+            ['43',  3, 0, RoundingMode::Up,          '4'],
+            ['43',  3, 0, RoundingMode::HalfUp,      '4'],
+            // V=91, n=3: 2^3·91 = 728 vs 9^3 = 729 (diff -1) → smallest "round down". ∛91 ≈ 4.4979.
+            ['91',  3, 0, RoundingMode::Unnecessary, 'NTH_ROOT_NOT_EXACT'],
+            ['91',  3, 0, RoundingMode::Down,        '4'],
+            ['91',  3, 0, RoundingMode::Up,          '5'],
+            ['91',  3, 0, RoundingMode::HalfUp,      '4'],
         ];
 
         foreach ($tests as [$number, $n, $scale, $roundingMode, $expected]) {

tests/BigIntegerTest.php

@@ -3939,31 +3939,26 @@ public static function providerNthRoot(): Generator
             // 2^100 is exact.
             ['1267650600228229401496703205376', 100, RoundingMode::Unnecessary, '2'],
 
-            // ∛17 ≈ 2.5713
-            ['17',  3, RoundingMode::Unnecessary, null],
-            ['17',  3, RoundingMode::Down,        '2'],
-            ['17',  3, RoundingMode::Up,          '3'],
-            ['17',  3, RoundingMode::HalfUp,      '3'],
-            // ∛16 ≈ 2.5198
-            ['16',  3, RoundingMode::Unnecessary, null],
-            ['16',  3, RoundingMode::Down,        '2'],
-            ['16',  3, RoundingMode::Up,          '3'],
-            ['16',  3, RoundingMode::HalfUp,      '3'],
-            // ∛864 ≈ 9.5224
-            ['864', 3, RoundingMode::Unnecessary, null],
-            ['864', 3, RoundingMode::Down,        '9'],
-            ['864', 3, RoundingMode::Up,          '10'],
-            ['864', 3, RoundingMode::HalfUp,      '10'],
-            // 8^¼ ≈ 1.6818
-            ['8',   4, RoundingMode::Unnecessary, null],
-            ['8',   4, RoundingMode::Down,        '1'],
-            ['8',   4, RoundingMode::Up,          '2'],
-            ['8',   4, RoundingMode::HalfUp,      '2'],
-            // ∛-17 ≈ -2.5713
-            ['-17', 3, RoundingMode::Unnecessary, null],
-            ['-17', 3, RoundingMode::Down,        '-2'],
-            ['-17', 3, RoundingMode::Up,          '-3'],
-            ['-17', 3, RoundingMode::HalfUp,      '-3'],
+            // Tightest possible Half* boundaries, where 2^n·|V| differs from (2·|t|+1)^n by ±1.
+            // V=43, n=3: 2^3·43 = 344 vs 7^3 = 343 (diff +1) → smallest "round up". ∛43 ≈ 3.5034.
+            ['43', 3, RoundingMode::Unnecessary, null],
+            ['43', 3, RoundingMode::Down, '3'],
+            ['43', 3, RoundingMode::Up, '4'],
+            ['43', 3, RoundingMode::HalfUp, '4'],
+            ['-43', 3, RoundingMode::Unnecessary, null],
+            ['-43', 3, RoundingMode::Down, '-3'],
+            ['-43', 3, RoundingMode::Up, '-4'],
+            ['-43', 3, RoundingMode::HalfUp, '-4'],
+
+            // V=91, n=3: 2^3·91 = 728 vs 9^3 = 729 (diff -1) → smallest "round down". ∛91 ≈ 4.4979.
+            ['91', 3, RoundingMode::Unnecessary, null],
+            ['91', 3, RoundingMode::Down, '4'],
+            ['91', 3, RoundingMode::Up, '5'],
+            ['91', 3, RoundingMode::HalfUp, '4'],
+            ['-91', 3, RoundingMode::Unnecessary, null],
+            ['-91', 3, RoundingMode::Down, '-4'],
+            ['-91', 3, RoundingMode::Up, '-5'],
+            ['-91', 3, RoundingMode::HalfUp, '-4'],
         ];
 
         foreach ($tests as [$number, $n, $roundingMode, $expected]) {