From aa003d1568b84372616e85b0295c1eb6b165c8a3 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?L=C5=91rinc?= <pap.lorinc@gmail.com>
Date: Thu, 12 Sep 2024 19:58:14 +0200
Subject: [PATCH] build: Minimize I/O operations in GenerateHeaderFromRaw.cmake

Replaced multiple file writes with a single string template write.
The raw content is first grouped into 8 byte chunks, followed by another regex replace which wraps them in `std::byte`.

Tested the output with `diff -w` and they're the same - only whitespace differences because slightly different source formatting.

Tested the performance with:
> time cmake -DRAW_SOURCE_PATH=src/bench/data/block413567.raw -DHEADER_PATH=build/after/block413567.raw.h -DRAW_NAMESPACE=benchmark::data -P cmake/script/GenerateHeaderFromRaw.cmake

Before:
> 15.41s user 23.06s system 97% cpu 39.593 total
After:
> 0.77s user 0.06s system 97% cpu 0.849 total
---
 cmake/script/GenerateHeaderFromRaw.cmake | 34 +++++++++++-------------
 1 file changed, 15 insertions(+), 19 deletions(-)

diff --git a/cmake/script/GenerateHeaderFromRaw.cmake b/cmake/script/GenerateHeaderFromRaw.cmake
index 18a6c2b4078..638876ecea1 100644
--- a/cmake/script/GenerateHeaderFromRaw.cmake
+++ b/cmake/script/GenerateHeaderFromRaw.cmake
@@ -2,26 +2,22 @@
 # Distributed under the MIT software license, see the accompanying
 # file COPYING or https://opensource.org/license/mit/.
 
+cmake_path(GET RAW_SOURCE_PATH STEM raw_source_basename)
+
 file(READ ${RAW_SOURCE_PATH} hex_content HEX)
-string(REGEX MATCHALL "([A-Za-z0-9][A-Za-z0-9])" bytes "${hex_content}")
+string(REGEX REPLACE "................" "\\0\n" formatted_bytes "${hex_content}")
+string(REGEX REPLACE "[^\n][^\n]" "std::byte{0x\\0}, " formatted_bytes "${formatted_bytes}")
 
-file(WRITE ${HEADER_PATH} "#include <cstddef>\n")
-file(APPEND ${HEADER_PATH} "#include <span>\n")
-file(APPEND ${HEADER_PATH} "namespace ${RAW_NAMESPACE} {\n")
-get_filename_component(raw_source_basename ${RAW_SOURCE_PATH} NAME_WE)
-file(APPEND ${HEADER_PATH} "inline constexpr std::byte detail_${raw_source_basename}_raw[]{\n")
+set(header_content
+"#include <cstddef>
+#include <span>
 
-set(i 0)
-foreach(byte ${bytes})
-  math(EXPR i "${i} + 1")
-  math(EXPR remainder "${i} % 8")
-  if(remainder EQUAL 0)
-    file(APPEND ${HEADER_PATH} "std::byte{0x${byte}},\n")
-  else()
-    file(APPEND ${HEADER_PATH} "std::byte{0x${byte}}, ")
-  endif()
-endforeach()
+namespace ${RAW_NAMESPACE} {
+inline constexpr std::byte detail_${raw_source_basename}_raw[] {
+${formatted_bytes}
+};
 
-file(APPEND ${HEADER_PATH} "\n};\n")
-file(APPEND ${HEADER_PATH} "inline constexpr std::span ${raw_source_basename}{detail_${raw_source_basename}_raw};\n")
-file(APPEND ${HEADER_PATH} "}")
+inline constexpr std::span ${raw_source_basename}{detail_${raw_source_basename}_raw};
+}
+")
+file(WRITE ${HEADER_PATH} "${header_content}")