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Trade control-flow dependency for data-dependency

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Removes branching in drawing code
This commit is contained in:
Michał Janiszewski
2016-02-20 17:10:09 +01:00
parent 14bf53bb30
commit 0e42bef94e
1 changed files with 25 additions and 28 deletions
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53
src/drawing/drawing_fast.cpp
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@@ -3,6 +3,9 @@ extern "C"
#include "drawing.h"
}
// This will have 1 for val > 0, 0 otherwise
#define greater_than_zero(val) (((val - 1) >> (sizeof(val) * 8 - 1)) + 1)
template<int image_type, int zoom_level>
static void FASTCALL DrawRLESprite2(const uint8* source_bits_pointer,
uint8* dest_bits_pointer,
@@ -24,9 +27,10 @@ static void FASTCALL DrawRLESprite2(const uint8* source_bits_pointer,
next_dest_pointer += line_width;
height -= zoom_amount;
}
const int source_y_end = height + source_y_start;
//For every line in the image
for (int y = source_y_start; y < (height + source_y_start); y += zoom_amount) {
for (int y = source_y_start; y < source_y_end; y += zoom_amount) {
//The first part of the source pointer is a list of offsets to different lines
//This will move the pointer to the correct source line.
@@ -52,39 +56,31 @@ static void FASTCALL DrawRLESprite2(const uint8* source_bits_pointer,
//Calculates the start point of the image
int x_start = gap_size - source_x_start;
const int x_diff = x_start & ~zoom_mask;
if (x_start & ~zoom_mask) {
no_pixels -= (x_start&~zoom_mask);
x_start += ~zoom_mask;
source_pointer += (x_start&~zoom_mask);
if (no_pixels <= 0) continue;
}
no_pixels -= x_diff;
x_start += ~zoom_mask * greater_than_zero(x_diff - 1);
source_pointer += (x_start&~zoom_mask);
if (x_start > 0) {
//Since the start is positive
//We need to move the drawing surface to the correct position
dest_pointer += x_start >> zoom_level;
} else {
//If the start is negative we require to remove part of the image.
//This is done by moving the image pointer to the correct position.
source_pointer -= x_start;
//The no_pixels will be reduced in this operation
no_pixels += x_start;
//If there are no pixels there is nothing to draw this data section
if (no_pixels <= 0) continue;
//Reset the start position to zero as we have taken into account all moves
x_start = 0;
}
// This will have 1 for x_start > 0, 0 otherwise
uint8 sign = greater_than_zero(x_start);
dest_pointer += (x_start >> zoom_level) * sign;
//If the start is negative we require to remove part of the image.
//This is done by moving the image pointer to the correct position.
source_pointer -= x_start * (1 - sign);
//The no_pixels will be reduced in this operation
no_pixels += x_start * (1 - sign);
//Reset the start position to zero as we have taken into account all moves
x_start *= sign;
int x_end = x_start + no_pixels;
//If the end position is further out than the whole image
//end position then we need to shorten the line again
if (x_end > width) {
//Shorten the line
no_pixels -= x_end - width;
//If there are no pixels there is nothing to draw.
if (no_pixels <= 0) continue;
}
const int pixels_till_end = x_end - width;
//Shorten the line
no_pixels -= pixels_till_end * greater_than_zero(pixels_till_end);
//Finally after all those checks, copy the image onto the drawing surface
//If the image type is not a basic one we require to mix the pixels
@@ -110,6 +106,7 @@ static void FASTCALL DrawRLESprite2(const uint8* source_bits_pointer,
} else
{
if (zoom_amount == 1) {
no_pixels *= greater_than_zero(no_pixels);
memcpy(dest_pointer, source_pointer, no_pixels);
} else {
for (; no_pixels > 0; no_pixels -= zoom_amount, source_pointer += zoom_amount, dest_pointer++) {