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Avoid slow modulo

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This commit is contained in:
Kornel Lesiński 2018-07-16 15:26:30 +01:00
parent 96889d6917
commit bb2aa4ce9b
2 changed files with 16 additions and 12 deletions
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16
src/reduction/alpha.rs
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@ -1,12 +1,14 @@
use png::PngData; use png::PngData;
pub fn reduce_alpha_channel(png: &mut PngData, channels: usize) -> Option<Vec<u8>> { pub fn reduce_alpha_channel(png: &mut PngData, channels: u8) -> Option<Vec<u8>> {
let byte_depth: u8 = png.ihdr_data.bit_depth.as_u8() >> 3; let byte_depth = png.ihdr_data.bit_depth.as_u8() >> 3;
let bpp: usize = channels * byte_depth as usize; let bpp = channels * byte_depth;
let colored_bytes = bpp - byte_depth as usize; let bpp_mask = bpp - 1;
assert_eq!(0, bpp & bpp_mask);
let colored_bytes = bpp - byte_depth;
for line in png.scan_lines() { for line in png.scan_lines() {
for (i, &byte) in line.data.iter().enumerate() { for (i, &byte) in line.data.iter().enumerate() {
if i % bpp >= colored_bytes { if i as u8 & bpp_mask >= colored_bytes {
if byte != 255 { if byte != 255 {
return None; return None;
} }
@ -18,7 +20,7 @@ pub fn reduce_alpha_channel(png: &mut PngData, channels: usize) -> Option<Vec<u8
for line in png.scan_lines() { for line in png.scan_lines() {
reduced.push(line.filter); reduced.push(line.filter);
for (i, &byte) in line.data.iter().enumerate() { for (i, &byte) in line.data.iter().enumerate() {
if i % bpp >= colored_bytes { if i as u8 & bpp_mask >= colored_bytes {
continue; continue;
} else { } else {
reduced.push(byte); reduced.push(byte);
@ -29,7 +31,7 @@ pub fn reduce_alpha_channel(png: &mut PngData, channels: usize) -> Option<Vec<u8
// sBIT contains information about alpha channel's original depth, // sBIT contains information about alpha channel's original depth,
// and alpha has just been removed // and alpha has just been removed
if let Some(sbit_header) = png.aux_headers.get_mut(&"sBIT".to_string()) { if let Some(sbit_header) = png.aux_headers.get_mut(&"sBIT".to_string()) {
assert_eq!(sbit_header.len(), channels); assert_eq!(sbit_header.len(), channels as usize);
sbit_header.pop(); sbit_header.pop();
} }

12
src/reduction/color.rs
View file

@ -16,16 +16,18 @@ pub fn reduce_rgba_to_rgb(png: &mut PngData) -> bool {
pub fn reduce_rgba_to_grayscale_alpha(png: &mut PngData) -> bool { pub fn reduce_rgba_to_grayscale_alpha(png: &mut PngData) -> bool {
let mut reduced = Vec::with_capacity(png.raw_data.len()); let mut reduced = Vec::with_capacity(png.raw_data.len());
let byte_depth: u8 = png.ihdr_data.bit_depth.as_u8() >> 3; let byte_depth = png.ihdr_data.bit_depth.as_u8() >> 3;
let bpp: usize = 4 * byte_depth as usize; let bpp = 4 * byte_depth;
let colored_bytes = bpp - byte_depth as usize; let bpp_mask = bpp - 1;
assert_eq!(0, bpp & bpp_mask);
let colored_bytes = bpp - byte_depth;
for line in png.scan_lines() { for line in png.scan_lines() {
reduced.push(line.filter); reduced.push(line.filter);
let mut low_bytes = Vec::with_capacity(4); let mut low_bytes = Vec::with_capacity(4);
let mut high_bytes = Vec::with_capacity(4); let mut high_bytes = Vec::with_capacity(4);
let mut trans_bytes = Vec::with_capacity(byte_depth as usize); let mut trans_bytes = Vec::with_capacity(byte_depth as usize);
for (i, byte) in line.data.iter().enumerate() { for (i, byte) in line.data.iter().enumerate() {
if i % bpp < colored_bytes { if i as u8 & bpp_mask < colored_bytes {
if byte_depth == 1 || i % 2 == 1 { if byte_depth == 1 || i % 2 == 1 {
low_bytes.push(*byte); low_bytes.push(*byte);
} else { } else {
@ -35,7 +37,7 @@ pub fn reduce_rgba_to_grayscale_alpha(png: &mut PngData) -> bool {
trans_bytes.push(*byte); trans_bytes.push(*byte);
} }
if i % bpp == bpp - 1 { if (i as u8 & bpp_mask) == bpp - 1 {
if low_bytes.iter().unique().count() > 1 { if low_bytes.iter().unique().count() > 1 {
return false; return false;
} }