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Fix overflowing multiplication leading to apparent hang

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closes #88
This commit is contained in:
sfan5 2022-02-08 23:35:23 +01:00
parent 9b26d9495c
commit 8e9805c3ff
1 changed files with 43 additions and 2 deletions
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45
TileGenerator.cpp
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@ -8,6 +8,8 @@
#include <stdexcept> #include <stdexcept>
#include <cstring> #include <cstring>
#include <vector> #include <vector>
#include <type_traits>
#include <limits>
#include "TileGenerator.h" #include "TileGenerator.h"
#include "config.h" #include "config.h"
@ -27,6 +29,10 @@
#include "db-redis.h" #include "db-redis.h"
#endif #endif
#ifndef __has_builtin
#define __has_builtin(x) 0
#endif
template<typename T> template<typename T>
static inline T mymax(T a, T b) static inline T mymax(T a, T b)
{ {
@ -39,6 +45,41 @@ static inline T mymin(T a, T b)
return (a > b) ? b : a; return (a > b) ? b : a;
} }
// saturating multiplication
template<typename T, class = typename std::enable_if<std::is_unsigned<T>::value>::type>
inline T sat_mul(T a, T b)
{
#if __has_builtin(__builtin_mul_overflow)
T res;
if (__builtin_mul_overflow(a, b, &res))
return std::numeric_limits<T>::max();
return res;
#else
const int bits = sizeof(T) * 8;
int hb_a = 0, hb_b = 0;
for (int i = bits - 1; i >= 0; i--) {
if (a & (static_cast<T>(1) << i)) {
hb_a = i; break;
}
}
for (int i = bits - 1; i >= 0; i--) {
if (b & (static_cast<T>(1) << i)) {
hb_b = i; break;
}
}
// log2(a) + log2(b) >= log2(MAX) <=> calculation will overflow
if (hb_a + hb_b >= bits)
return std::numeric_limits<T>::max();
return a * b;
#endif
}
template<typename T>
inline T sat_mul(T a, T b, T c)
{
return sat_mul(sat_mul(a, b), c);
}
// rounds n (away from 0) to a multiple of f while preserving the sign of n // rounds n (away from 0) to a multiple of f while preserving the sign of n
static int round_multiple_nosign(int n, int f) static int round_multiple_nosign(int n, int f)
{ {
@ -357,7 +398,7 @@ void TileGenerator::openDb(const std::string &input)
// Determine how we're going to traverse the database (heuristic) // Determine how we're going to traverse the database (heuristic)
if (m_exhaustiveSearch == EXH_AUTO) { if (m_exhaustiveSearch == EXH_AUTO) {
size_t y_range = (m_yMax / 16 + 1) - (m_yMin / 16); size_t y_range = (m_yMax / 16 + 1) - (m_yMin / 16);
size_t blocks = (m_geomX2 - m_geomX) * y_range * (m_geomY2 - m_geomY); size_t blocks = sat_mul<size_t>(m_geomX2 - m_geomX, y_range, m_geomY2 - m_geomY);
#ifndef NDEBUG #ifndef NDEBUG
std::cerr << "Heuristic parameters:" std::cerr << "Heuristic parameters:"
<< " preferRangeQueries()=" << m_db->preferRangeQueries() << " preferRangeQueries()=" << m_db->preferRangeQueries()
@ -416,7 +457,7 @@ void TileGenerator::loadBlocks()
m_positions[pos.z].emplace(pos.x); m_positions[pos.z].emplace(pos.x);
} }
int count = 0; size_t count = 0;
for (const auto &it : m_positions) for (const auto &it : m_positions)
count += it.second.size(); count += it.second.size();
m_progressMax = count; m_progressMax = count;