[GitHub] [arrow] projjal commented on a change in pull request #10195: ARROW-12595: [C++][Gandiva] Implement TO_HEX([binary] field), HEX, UNHEX and FROM_HEX([string]field] functions

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

projjal commented on a change in pull request #10195:
URL: https://github.com/apache/arrow/pull/10195#discussion_r664633954



##########
File path: cpp/src/gandiva/precompiled/string_ops.cc
##########
@@ -2072,4 +2074,102 @@ const char* byte_substr_binary_int32_int32(gdv_int64 context, const char* text,
   memcpy(ret, text + startPos, *out_len);
   return ret;
 }
+
+// Gets a binary object and returns its hexadecimal representation. That representation
+// maps each byte in the input to a 2-length string containing a hexadecimal number.
+// - Examples:
+//     - foo -> 666F6F = 66[f] 6F[o] 6F[o]
+//     - bar -> 626172 = 62[b] 61[a] 72[r]
+FORCE_INLINE
+const char* to_hex_binary(int64_t context, const char* text, int32_t text_len,
+                          int32_t* out_len) {
+  if (text_len == 0) {
+    *out_len = 0;
+    return "";
+  }
+
+  auto ret =
+      reinterpret_cast<char*>(gdv_fn_context_arena_malloc(context, text_len * 2 + 1));
+
+  if (ret == nullptr) {
+    gdv_fn_context_set_error_msg(context, "Could not allocate memory for output string");
+    *out_len = 0;
+    return "";
+  }
+
+  uint32_t ret_index = 0;
+  uint32_t max_len = static_cast<uint32_t>(text_len) * 2;
+  uint32_t max_char_to_write = 4;
+
+  for (gdv_int32 i = 0; i < text_len; i++) {
+    DCHECK(ret_index >= 0 && ret_index < max_len);
+
+    int32_t ch = static_cast<int32_t>(text[i]) & 0xFF;
+
+    ret_index += snprintf(ret + ret_index, max_char_to_write, "%02X", ch);
+  }
+
+  *out_len = static_cast<int32_t>(ret_index);
+  return ret;
+}
+
+FORCE_INLINE
+const char* to_hex_big_int(int64_t context, int64_t data, int32_t* out_len) {
+  const int64_t hex_long_max_size = 2 * sizeof(int64_t);
+  auto ret =
+      reinterpret_cast<char*>(gdv_fn_context_arena_malloc(context, hex_long_max_size));
+
+  if (ret == nullptr) {
+    gdv_fn_context_set_error_msg(context, "Could not allocate memory for output string");
+    *out_len = 0;
+    return "";
+  }
+  snprintf(ret, hex_long_max_size + 1, "%0" PRIX64, data);

Review comment:
       shouldn't it be "0x%" PRIX64?
   This is also probably why build is failing in some env




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