util/HexFormat: faster implementation without snprintf()

src/util/HexFormat.cxx

@@ -1,43 +0,0 @@
-/*
- * Copyright (C) 2018 Max Kellermann <max.kellermann@gmail.com>
- *
- * Redistribution and use in source and binary forms, with or without
- * modification, are permitted provided that the following conditions
- * are met:
- *
- * - Redistributions of source code must retain the above copyright
- * notice, this list of conditions and the following disclaimer.
- *
- * - Redistributions in binary form must reproduce the above copyright
- * notice, this list of conditions and the following disclaimer in the
- * documentation and/or other materials provided with the
- * distribution.
- *
- * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
- * ``AS IS'' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
- * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
- * FOR A PARTICULAR PURPOSE ARE DISCLAIMED.  IN NO EVENT SHALL THE
- * FOUNDATION OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
- * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES
- * (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR
- * SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
- * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT,
- * STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE)
- * ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED
- * OF THE POSSIBILITY OF SUCH DAMAGE.
- */
-
-#include "HexFormat.hxx"
-
-#include <stdio.h>
-
-char *
-HexFormat(char *dest, ConstBuffer<uint8_t> src) noexcept
-{
-	for (auto i : src) {
-		sprintf(dest, "%02x", i);
-		dest += 2;
-	}
-
-	return dest;
-}

src/util/HexFormat.hxx

@@ -1,5 +1,8 @@
 /*
- * Copyright (C) 2018 Max Kellermann <max.kellermann@gmail.com>
+ * Copyright 2007-2022 CM4all GmbH
+ * All rights reserved.
+ *
+ * author: Max Kellermann <mk@cm4all.com>
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
@@ -27,8 +30,7 @@
  * OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
-#ifndef HEX_FORMAT_HXX
+#pragma once
-#define HEX_FORMAT_HXX
 
 #include "ConstBuffer.hxx"
 #include "StringBuffer.hxx"
@@ -36,16 +38,67 @@
 #include <cstddef>
 #include <cstdint>
 
+constexpr char hex_digits[] = "0123456789abcdef";
+
+[[gnu::always_inline]]
+static constexpr char *
+HexFormatUint8Fixed(char dest[2], uint8_t number) noexcept
+{
+	dest[0] = hex_digits[(number >> 4) & 0xf];
+	dest[1] = hex_digits[number & 0xf];
+	return dest + 2;
+}
+
+[[gnu::always_inline]]
+static constexpr char *
+HexFormatUint16Fixed(char dest[4], uint16_t number) noexcept
+{
+	dest[0] = hex_digits[(number >> 12) & 0xf];
+	dest[1] = hex_digits[(number >> 8) & 0xf];
+	dest[2] = hex_digits[(number >> 4) & 0xf];
+	dest[3] = hex_digits[number & 0xf];
+	return dest + 4;
+}
+
+[[gnu::always_inline]]
+static constexpr char *
+HexFormatUint32Fixed(char dest[8], uint32_t number) noexcept
+{
+	dest[0] = hex_digits[(number >> 28) & 0xf];
+	dest[1] = hex_digits[(number >> 24) & 0xf];
+	dest[2] = hex_digits[(number >> 20) & 0xf];
+	dest[3] = hex_digits[(number >> 16) & 0xf];
+	dest[4] = hex_digits[(number >> 12) & 0xf];
+	dest[5] = hex_digits[(number >> 8) & 0xf];
+	dest[6] = hex_digits[(number >> 4) & 0xf];
+	dest[7] = hex_digits[number & 0xf];
+	return dest + 8;
+}
+
+[[gnu::always_inline]]
+static constexpr char *
+HexFormatUint64Fixed(char dest[16], uint64_t number) noexcept
+{
+	dest = HexFormatUint32Fixed(dest, number >> 32);
+	dest = HexFormatUint32Fixed(dest, number);
+	return dest;
+}
+
 /**
- * Format the given byte sequence into a null-terminated hexadecimal
+ * Format the given input buffer of bytes to hex.  The caller ensures
- * string.
+ * that the output buffer is at least twice as large as the input.
+ * Does not null-terminate the output buffer.
  *
- * @param dest the destination buffer; must be large enough to hold
+ * @return a pointer to one after the last written character
- * all hex digits plus the null terminator
- * @return a pointer to the generated null terminator
  */
-char *
+constexpr char *
-HexFormat(char *dest, ConstBuffer<uint8_t> src) noexcept;
+HexFormat(char *output, ConstBuffer<uint8_t> input) noexcept
+{
+	for (const auto &i : input)
+		output = HexFormatUint8Fixed(output, i);
+
+	return output;
+}
 
 /**
  * Like HexFormat(), but return a #StringBuffer with exactly the
@@ -53,12 +106,10 @@ HexFormat(char *dest, ConstBuffer<uint8_t> src) noexcept;
  */
 template<size_t size>
 [[gnu::pure]]
-auto
+constexpr auto
 HexFormatBuffer(const uint8_t *src) noexcept
 {
 	StringBuffer<size * 2 + 1> dest;
-	HexFormat(dest.data(), {src, size});
+	*HexFormat(dest.data(), {src, size}) = 0;
 	return dest;
 }
-
-#endif

src/util/meson.build

@@ -2,7 +2,6 @@ util = static_library(
   'util',
   'Exception.cxx',
   'UTF8.cxx',
-  'HexFormat.cxx',
   'MimeType.cxx',
   'NumberParser.cxx',
   'StringView.cxx',