[GitHub] [arrow] pravindra commented on a change in pull request #7402: ARROW-9099: [C++][Gandiva] Implement trim function for string

[GitBox <gi...@apache.org>]

pravindra commented on a change in pull request #7402:
URL: https://github.com/apache/arrow/pull/7402#discussion_r442867225



##########
File path: cpp/src/gandiva/precompiled/string_ops.cc
##########
@@ -284,6 +284,49 @@ const char* reverse_utf8(gdv_int64 context, const char* data, gdv_int32 data_len
   return ret;
 }
 
+// Trim a utf8 sequence
+FORCE_INLINE
+const char* trim_utf8(gdv_int64 context, const char* data, gdv_int32 data_len,
+                      int32_t* out_len) {
+  if (data_len == 0) {
+    *out_len = 0;
+    return "";
+  }
+
+  gdv_int32 start = 0, end = data_len - 1;
+  // start and end denote the first and last positions of non-space
+  // characters in the input string respectively
+  while (start <= end && data[start] == ' ') {
+    ++start;
+  }
+  while (end >= start && data[end] == ' ') {
+    --end;
+  }
+
+  // string with no leading/trailing spaces, return original string
+  if (start == 0 && end == data_len - 1) {
+    *out_len = data_len;
+    return data;
+  }
+
+  // string with all spaces
+  if (start > end) {
+    *out_len = 0;
+    return "";
+  }
+
+  gdv_int32 length = end - start + 1;
+  char* ret = reinterpret_cast<char*>(gdv_fn_context_arena_malloc(context, length));

Review comment:
       why malloc and copy ? you could do 
   
   *out_len = length;
   return data + start;




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