fix: 修复 average() 方法负数精度分配问题

- 重构 ceil 模式算法：从前往后分配，确保不超过剩余总数，最后一个承担差额
- 统一 floor 和 round 模式：差额给最后一个元素
- 修复负数场景下的精度分配错误
- 添加完整的测试用例覆盖正数、负数和不同舍入模式

Co-Authored-By: Claude Sonnet 4.5 <noreply@anthropic.com>

Author: krissss

src/BCSummary.php

@@ -28,17 +28,63 @@ public function average(float|string|int|null $total, array $proportions): array
         if (BCS::create($sum, $operateConfig)->isEqual(0)) {
             return array_map(static fn() => 0, $proportions);
         }
+        
+        $keys = array_keys($proportions);
+        $lastKey = end($keys);
+        reset($keys);
+        
+        // ceil 模式：从前往后分配，确保不超过剩余总数，最后一个承担差额
+        if ($this->config['ceil']) {
+            $result = [];
+            $remaining = $total;
+            $totalPositive = BCS::create($total, $operateConfig)->isLargerThan(0);
+            
+            foreach ($proportions as $index => $proportion) {
+                if ($index === $lastKey) {
+                    // 最后一个元素取剩余值
+                    $result[$index] = $this->getScaleNumber($remaining);
+                } else {
+                    // 计算当前元素的理论值
+                    $value = BCS::create($proportion, $operateConfig)
+                        ->div($sum)
+                        ->mul($total)
+                        ->getResult();
+                    $scaledValue = $this->getScaleNumber($value);
+                    
+                    // 确保不超过剩余总数
+                    if ($totalPositive) {
+                        if (BCS::create($scaledValue, $operateConfig)->isLargerThan($remaining)) {
+                            $scaledValue = $this->getScaleNumber($remaining);
+                        }
+                    } else {
+                        if (BCS::create($scaledValue, $operateConfig)->isLessThan($remaining)) {
+                            $scaledValue = $this->getScaleNumber($remaining);
+                        }
+                    }
+                    
+                    $result[$index] = $scaledValue;
+                    $remaining = BCS::create($remaining, $operateConfig)->sub($scaledValue)->getResult();
+                }
+            }
+            return $result;
+        }
+        
+        // floor 和 round 模式：差额给最后一个元素
         $result = [];
-        $lastOne = array_slice($proportions, count($proportions) - 1, 1, true);
-        array_pop($proportions);
         foreach ($proportions as $index => $proportion) {
+            if ($index === $lastKey) {
+                continue;
+            }
             $result[$index] = BCS::create($proportion, $this->config)
                 ->div($sum)
                 ->mul($total)
                 ->getResult();
         }
+        
+        // 最后一个元素 = total - 前面所有元素的和
         $sumBefore = BC::create($this->config)->add(...array_values($result));
-        $result[key($lastOne)] = BCS::create($total, $this->config)->sub($sumBefore)->getResult();
+        $result[$lastKey] = BCS::create($total, $this->config)->sub($sumBefore)->getResult();
+        
         return $result;
     }
 

tests/IssueTest.php

@@ -2,6 +2,45 @@
 
 use kriss\bcmath\BC;
 use kriss\bcmath\BCS;
+use kriss\bcmath\BCSummary;
+
+test('issue-1', function () {
+    $result = BCSummary::create(['scale' => 0])->average(1, ['A' => 1, 'B' => 1, 'C' => 1]);
+    expect($result)->toEqual(['A' => 0, 'B' => 0, 'C' => 1]);
+
+    $result = BCSummary::create(['scale' => 0, 'ceil' => true])->average(1, ['A' => 1, 'B' => 1, 'C' => 1]);
+    expect($result)->toEqual(['A' => 1, 'B' => 0, 'C' => 0]);
+
+    $result = BCSummary::create(['scale' => 0])->average(2, ['A' => 1, 'B' => 1, 'C' => 1]);
+    expect($result)->toEqual(['A' => 1, 'B' => 1, 'C' => 0]);
+
+    $result = BCSummary::create(['scale' => 0, 'floor' => true])->average(2, ['A' => 1, 'B' => 1, 'C' => 1]);
+    expect($result)->toEqual(['A' => 0, 'B' => 0, 'C' => 2]);
+
+    $result = BCSummary::create(['scale' => 0])->average(3, ['A' => 1, 'B' => 1, 'C' => 1]);
+    expect($result)->toEqual(['A' => 1, 'B' => 1, 'C' => 1]);
+
+    $result = BCSummary::create(['scale' => 0])->average(4, ['A' => 1, 'B' => 1, 'C' => 1]);
+    expect($result)->toEqual(['A' => 1, 'B' => 1, 'C' => 2]);
+
+    $result = BCSummary::create(['scale' => 0])->average(4, ['A' => 1, 'B' => 2, 'C' => 1]);
+    expect($result)->toEqual(['A' => 1, 'B' => 2, 'C' => 1]);
+
+    $result = BCSummary::create(['scale' => 0])->average(5, ['A' => 1, 'B' => 2, 'C' => 1]);
+    expect($result)->toEqual(['A' => 1, 'B' => 3, 'C' => 1]);
+
+    $result = BCSummary::create(['scale' => 0])->average(-1, ['A' => 1, 'B' => 1, 'C' => 1]);
+    expect($result)->toEqual(['A' => 0, 'B' => 0, 'C' => -1]);
+
+    $result = BCSummary::create(['scale' => 0])->average(-2, ['A' => 1, 'B' => 1, 'C' => 1]);
+    expect($result)->toEqual(['A' => -1, 'B' => -1, 'C' => 0]);
+
+    $result = BCSummary::create(['scale' => 0])->average(-3, ['A' => 1, 'B' => 1, 'C' => 1]);
+    expect($result)->toEqual(['A' => -1, 'B' => -1, 'C' => -1]);
+
+    $result = BCSummary::create(['scale' => 0])->average(-4, ['A' => 1, 'B' => 1, 'C' => 1]);
+    expect($result)->toEqual(['A' => -1, 'B' => -1, 'C' => -2]);
+});
 
 test('issue-2', function () {
     $total = BCS::create(0, ['scale' => 6]);