From fe3844f5446160f3663d7c5f2ef5930c083fdf0a Mon Sep 17 00:00:00 2001
From: Abdullah Javed Nesar <abduljaved1994@gmail.com>
Date: Sat, 30 Apr 2022 23:16:22 +0530
Subject: [PATCH] Implementation for negative indexing in str

---
 integration_tests/test_str_01.py         | 2 ++
 src/runtime/impure/lfortran_intrinsics.c | 7 +++++++
 2 files changed, 9 insertions(+)

diff --git a/integration_tests/test_str_01.py b/integration_tests/test_str_01.py
index 5752c3267a..7da6cd83bc 100644
--- a/integration_tests/test_str_01.py
+++ b/integration_tests/test_str_01.py
@@ -24,6 +24,8 @@ def test_str_index():
     a: str
     a = "012345"
     assert a[2] == "2"
+    assert a[-1] == "5"
+    assert a[-6] == "0"
 
 def check():
     f()
diff --git a/src/runtime/impure/lfortran_intrinsics.c b/src/runtime/impure/lfortran_intrinsics.c
index 7b4747c6bb..63f8b2535d 100644
--- a/src/runtime/impure/lfortran_intrinsics.c
+++ b/src/runtime/impure/lfortran_intrinsics.c
@@ -616,6 +616,13 @@ LFORTRAN_API void _lfortran_strcat(char** s1, char** s2, char** dest)
 
 // idx1 and idx2 both start from 1
 LFORTRAN_API char* _lfortran_str_copy(char* s, int32_t idx1, int32_t idx2) {
+    int s_len = strlen(s);
+    if(idx1 <= 0) {
+        idx1 = s_len + idx1;
+    }
+    if(idx2 <= 0) {
+        idx2 = s_len + idx2;
+    }
     char* dest_char = (char*)malloc(idx2-idx1+2);
     for (int i=idx1; i <= idx2; i++)
     {