Fix some edge cases for compile time operations of % operator (#1566)

Author: faze-geek

integration_tests/expr_05.py

@@ -11,6 +11,8 @@ def main0():
     b: i32
     a = 10
     b = -5
+    eps: f64
+    eps = 1e-12
     assert test_multiply(a, b) == -50
     i: i64
     i = i64(1)
@@ -69,6 +71,12 @@ def main0():
     assert a == 0
     b **= 4
     assert b == 256
+    # Test Issue 1562
+    assert ((-8)%3) == 1
+    assert ((8)%-3) == -1
+    assert (-8%-3) == -2
+    assert abs((11.0%-3.0) - (-1.0)) < eps
+    assert abs((-11.0%3.0) - (1.0)) < eps
 
 
 main0()

src/lpython/semantics/python_comptime_eval.h

@@ -211,13 +211,24 @@ struct PythonIntrinsicProcedures {
         if (ASRUtils::is_integer(*type)) {
             int64_t a = ASR::down_cast<ASR::IntegerConstant_t>(arg1)->m_n;
             int64_t b = ASR::down_cast<ASR::IntegerConstant_t>(arg2)->m_n;
+            if(b == 0) { // Zero Division
+                throw SemanticError("Integer division or modulo by zero",loc);
+            }
+
+            // Refer the following link to understand how modulo in C++ is modified to behave like Python.
+            // https://stackoverflow.com/questions/1907565/c-and-python-different-behaviour-of-the-modulo-operation
             return ASR::down_cast<ASR::expr_t>(
-                ASR::make_IntegerConstant_t(al, loc, a%b, type));
+                ASR::make_IntegerConstant_t(al, loc, ((a%b)+b)%b, type));
         } else if (ASRUtils::is_real(*type)) {
             double a = ASR::down_cast<ASR::RealConstant_t>(arg1)->m_r;
             double b = ASR::down_cast<ASR::RealConstant_t>(arg2)->m_r;
+            if (b == 0) { // Zero Division
+                throw SemanticError("Float division or modulo by zero", loc);
+            }
+
+            // https://stackoverflow.com/questions/1907565/c-and-python-different-behaviour-of-the-modulo-operation
             return ASR::down_cast<ASR::expr_t>(
-                ASR::make_RealConstant_t(al, loc, std::fmod(a, b), type));
+                ASR::make_RealConstant_t(al, loc, std::fmod(std::fmod(a, b) + b, b), type));
         } else {
             throw SemanticError("_mod() must have both integer or both real arguments.", loc);
         }

tests/reference/asr-expr_05-3a37324.json

@@ -2,11 +2,11 @@
     "basename": "asr-expr_05-3a37324",
     "cmd": "lpython --show-asr --no-color {infile} -o {outfile}",
     "infile": "tests/../integration_tests/expr_05.py",
-    "infile_hash": "e391b0795af9d77b92cd60ce235d00761db224f5056cab55cb6278c2",
+    "infile_hash": "59668f790720eb827bd2963bb57a934805aa5139fff582a3b138a8e4",
     "outfile": null,
     "outfile_hash": null,
     "stdout": "asr-expr_05-3a37324.stdout",
-    "stdout_hash": "e9ee5559639de0903d652344a2e091fe76c25f5e6d57bcb0d30f8554",
+    "stdout_hash": "6ee2e60ba4c39354eb284734d4588f8197a52a75634e49fceda63ec3",
     "stderr": null,
     "stderr_hash": null,
     "returncode": 0