source/spirv_endian.cpp

   1 // Copyright (c) 2015-2016 The Khronos Group Inc.
   2 //
   3 // Licensed under the Apache License, Version 2.0 (the "License");
   4 // you may not use this file except in compliance with the License.
   5 // You may obtain a copy of the License at
   6 //
   7 //     http://www.apache.org/licenses/LICENSE-2.0
   8 //
   9 // Unless required by applicable law or agreed to in writing, software
  10 // distributed under the License is distributed on an "AS IS" BASIS,
  11 // WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
  12 // See the License for the specific language governing permissions and
  13 // limitations under the License.
  14
  15 #include "source/spirv_endian.h"
  16
  17 #include <cstring>
  18
  19 enum {
  20   I32_ENDIAN_LITTLE = 0x03020100ul,
  21   I32_ENDIAN_BIG = 0x00010203ul,
  22 };
  23
  24 // This constant value allows the detection of the host machine's endianness.
  25 // Accessing it through the "value" member is valid due to C++11 section 3.10
  26 // paragraph 10.
  27 static const union {
  28   unsigned char bytes[4];
  29   uint32_t value;
  30 } o32_host_order = {{0, 1, 2, 3}};
  31
  32 #define I32_ENDIAN_HOST (o32_host_order.value)
  33
  34 uint32_t spvFixWord(const uint32_t word, const spv_endianness_t endian) {
  35   if ((SPV_ENDIANNESS_LITTLE == endian && I32_ENDIAN_HOST == I32_ENDIAN_BIG) ||
  36       (SPV_ENDIANNESS_BIG == endian && I32_ENDIAN_HOST == I32_ENDIAN_LITTLE)) {
  37     return (word & 0x000000ff) << 24 | (word & 0x0000ff00) << 8 |
  38            (word & 0x00ff0000) >> 8 | (word & 0xff000000) >> 24;
  39   }
  40
  41   return word;
  42 }
  43
  44 uint64_t spvFixDoubleWord(const uint32_t low, const uint32_t high,
  45                           const spv_endianness_t endian) {
  46   return (uint64_t(spvFixWord(high, endian)) << 32) | spvFixWord(low, endian);
  47 }
  48
  49 spv_result_t spvBinaryEndianness(spv_const_binary binary,
  50                                  spv_endianness_t* pEndian) {
  51   if (!binary->code || !binary->wordCount) return SPV_ERROR_INVALID_BINARY;
  52   if (!pEndian) return SPV_ERROR_INVALID_POINTER;
  53
  54   uint8_t bytes[4];
  55   memcpy(bytes, binary->code, sizeof(uint32_t));
  56
  57   if (0x03 == bytes[0] && 0x02 == bytes[1] && 0x23 == bytes[2] &&
  58       0x07 == bytes[3]) {
  59     *pEndian = SPV_ENDIANNESS_LITTLE;
  60     return SPV_SUCCESS;
  61   }
  62
  63   if (0x07 == bytes[0] && 0x23 == bytes[1] && 0x02 == bytes[2] &&
  64       0x03 == bytes[3]) {
  65     *pEndian = SPV_ENDIANNESS_BIG;
  66     return SPV_SUCCESS;
  67   }
  68
  69   return SPV_ERROR_INVALID_BINARY;
  70 }
  71
  72 bool spvIsHostEndian(spv_endianness_t endian) {
  73   return ((SPV_ENDIANNESS_LITTLE == endian) &&
  74           (I32_ENDIAN_LITTLE == I32_ENDIAN_HOST)) ||
  75          ((SPV_ENDIANNESS_BIG == endian) &&
  76           (I32_ENDIAN_BIG == I32_ENDIAN_HOST));
  77 }