ARROW-15699: [C++][Gandiva] Fix implementation of left and right func…

…tions to handle more cases

Proper handling of multibyte characters

Added conditions to handle below cases:
case where left('abcdef', -6) -> "" and left('abcdef', -7) -> ""
case where right('abcdef', -6) -> "" and right('abcdef', -7) -> ""

cpp/src/gandiva/precompiled/string_ops.cc

@@ -2172,7 +2172,7 @@ const char* left_utf8_int32(gdv_int64 context, const char* text, gdv_int32 text_
   }
 
   // case where left('abcdef', -6) -> "" and left('abcdef', -7) -> ""
-  if(number < 0 && abs(number) >= char_count) {
+  if(number < 0 && -(number) >= char_count) {
     *out_len = 0;
     return "";
   }
@@ -2223,13 +2223,12 @@ const char* right_utf8_int32(gdv_int64 context, const char* text, gdv_int32 text
   }
 
   //case where right('abcdef', -6) -> "" and right('abcdef', -7) -> ""
-  if(number < 0 && abs(number) >= char_count) {
+  if(number < 0 && -(number) >= char_count) {
     *out_len = 0;
     return "";
   }
 
   int32_t start_char_pos;  // the char result start position (inclusive)
-  int32_t end_pos;    // the char result end position (inclusive)
 
   if (number > 0) {
     // case where right('abc', 5) ==> 'abc' start_char_pos=1.
@@ -2238,26 +2237,13 @@ const char* right_utf8_int32(gdv_int64 context, const char* text, gdv_int32 text
     start_char_pos = number * -1;
   }
 
-  end_pos = char_count;
-
-  // calculate the start byte and end byte position
+  // calculate the start byte position
   int32_t start_byte_pos = utf8_byte_pos(context, text, text_len, start_char_pos);
-  int32_t end_byte_pos = utf8_byte_pos(context, text, text_len, end_pos);
 
   //calculate output length
-  *out_len = (end_byte_pos - start_byte_pos);
+  *out_len = (text_len - start_byte_pos);
 
-  // try to allocate memory for the response
-  char* ret =
-      reinterpret_cast<gdv_binary>(gdv_fn_context_arena_malloc(context, *out_len));
-  if (ret == nullptr) {
-    gdv_fn_context_set_error_msg(context, "Could not allocate memory for output string");
-    *out_len = 0;
-    return "";
-  }
-
-  memcpy(ret, text + start_byte_pos, *out_len);
-  return ret;
+  return text + start_byte_pos;
 }
 
 FORCE_INLINE