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(svn r11559) -Fix [FS#1505]: overflow when drawing graphics with high company values.

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rubidium 2007-12-02 19:21:56 +00:00
parent 49e6247de8
commit 8c0122f429
3 changed files with 53 additions and 7 deletions
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28
src/core/bitmath_func.cpp
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@ -25,7 +25,7 @@ const uint8 _ffb_64[64] = {
* way further. If no bit is set return 0.
*
* @param x The value to search
* @param The position of the first bit set
* @return The position of the first bit set
*/
uint8 FindFirstBit(uint32 x)
{
@ -43,3 +43,29 @@ uint8 FindFirstBit(uint32 x)
return pos;
}
/**
* Search the last set bit in a 32 bit variable.
*
* This algorithm is a static implementation of a log
* conguence search algorithm. It checks the first half
* if there is a bit set search there further. And this
* way further. If no bit is set return 0.
*
* @param x The value to search
* @return The position of the last bit set
*/
uint8 FindLastBit(uint32 x)
{
if (x == 0) return 0;
uint8 pos = 0;
if ((x & 0xffff0000) != 0) { x >>= 16; pos += 16; }
if ((x & 0x0000ff00) != 0) { x >>= 8; pos += 8; }
if ((x & 0x000000f0) != 0) { x >>= 4; pos += 4; }
if ((x & 0x0000000c) != 0) { x >>= 2; pos += 2; }
if ((x & 0x00000002) != 0) { pos += 1; }
return pos;
}

1
src/core/bitmath_func.hpp
View File

@ -211,6 +211,7 @@ static inline uint8 FindFirstBit2x64(const int value)
}
uint8 FindFirstBit(uint32 x);
uint8 FindLastBit(uint32 x);
/**
* Clear the first bit in an integer.

31
src/graph_gui.cpp
View File

@ -65,7 +65,7 @@ struct GraphDrawer {
uint height; ///< The height of the graph in pixels.
StringID format_str_y_axis;
byte colors[GRAPH_MAX_DATASETS];
Money cost[GRAPH_MAX_DATASETS][24]; ///< last 2 years
OverflowSafeInt64 cost[GRAPH_MAX_DATASETS][24]; ///< last 2 years
};
static void DrawGraph(const GraphDrawer *gw)
@ -133,7 +133,7 @@ static void DrawGraph(const GraphDrawer *gw)
for (int i = 0; i < gw->num_dataset; i++) {
if (!HasBit(gw->excluded_data, i)) {
for (int j = 0; j < gw->num_on_x_axis; j++) {
Money datapoint = gw->cost[i][j];
OverflowSafeInt64 datapoint = gw->cost[i][j];
if (datapoint != INVALID_DATAPOINT) {
/* For now, if the graph has negative values the scaling is
@ -215,12 +215,31 @@ static void DrawGraph(const GraphDrawer *gw)
uint prev_y = INVALID_DATAPOINT_POS;
for (int j = 0; j < gw->num_on_x_axis; j++) {
Money datapoint = gw->cost[i][j];
OverflowSafeInt64 datapoint = gw->cost[i][j];
if (datapoint != INVALID_DATAPOINT) {
/* XXX: This can overflow if x_axis_offset * datapoint is
* too big to fit in an int64. */
y = gw->top + x_axis_offset - (x_axis_offset * datapoint) / highest_value;
/*
* Check whether we need to reduce the 'accuracy' of the
* datapoint value and the highest value to splut overflows.
* And when 'drawing' 'one million' or 'one million and one'
* there is no significant difference, so the least
* significant bits can just be removed.
*
* If there are more bits needed than would fit in a 32 bits
* integer, so at about 31 bits because of the sign bit, the
* least significant bits are removed.
*/
int mult_range = FindLastBit(x_axis_offset) + FindLastBit(abs(datapoint));
int reduce_range = max(mult_range - 31, 0);
/* Handle negative values differently (don't shift sign) */
if (datapoint < 0) {
datapoint = -(abs(datapoint) >> reduce_range);
} else {
datapoint >>= reduce_range;
}
y = gw->top + x_axis_offset - (x_axis_offset * datapoint) / (highest_value >> reduce_range);
/* Draw the point. */
GfxFillRect(x - 1, y - 1, x + 1, y + 1, color);