From 1c88b82dfc0773b3c25b46dd5a0b01017c2ad40a Mon Sep 17 00:00:00 2001
From: Nico Weber <thakis@chromium.org>
Date: Sat, 2 Dec 2023 19:28:18 +0900
Subject: [PATCH] LibPDF: Do less work in SampledFunction::evaluate()'s inner
 loop

Instead of recomputing the left index and the float amount in that
interval for each coordinate all the time, do it once when we
preprocess the input coordinates.

One line less, faster, and arguably easier to read.

No behavior change.
---
 Userland/Libraries/LibPDF/Function.cpp | 21 ++++++++++-----------
 1 file changed, 10 insertions(+), 11 deletions(-)

diff --git a/Userland/Libraries/LibPDF/Function.cpp b/Userland/Libraries/LibPDF/Function.cpp
index 561d2799fe..679e2b76ff 100644
--- a/Userland/Libraries/LibPDF/Function.cpp
+++ b/Userland/Libraries/LibPDF/Function.cpp
@@ -68,6 +68,7 @@ private:
     ReadonlyBytes m_sample_data;
 
     Vector<float> mutable m_inputs;
+    Vector<unsigned> mutable m_left_index;
     Vector<float> mutable m_outputs;
 };
 
@@ -167,6 +168,7 @@ SampledFunction::create(Document* document, Vector<Bound> domain, Optional<Vecto
     function->m_encode = move(encode);
     function->m_decode = move(decode);
     function->m_inputs.resize(function->m_domain.size());
+    function->m_left_index.resize(function->m_domain.size());
     function->m_outputs.resize(function->m_range.size());
     return function;
 }
@@ -189,8 +191,11 @@ PDFErrorOr<ReadonlySpan<float>> SampledFunction::evaluate(ReadonlySpan<float> xs
     for (size_t i = 0; i < m_domain.size(); ++i) {
         float x = clamp(xs[i], m_domain[i].lower, m_domain[i].upper);
         float e = interpolate(x, m_domain[i].lower, m_domain[i].upper, m_encode[i].lower, m_encode[i].upper);
-        float ec = clamp(e, 0.0f, static_cast<float>(m_sizes[i] - 1));
-        m_inputs[i] = ec;
+
+        unsigned n = m_sizes[i] - 1;
+        float ec = clamp(e, 0.0f, static_cast<float>(n));
+        m_left_index[i] = min(ec, n - 1);
+        m_inputs[i] = ec - m_left_index[i];
     }
 
     for (size_t r = 0; r < m_range.size(); ++r) {
@@ -207,20 +212,14 @@ PDFErrorOr<ReadonlySpan<float>> SampledFunction::evaluate(ReadonlySpan<float> xs
         Vector<int> coordinates;
         coordinates.resize(m_domain.size());
         for (size_t mask = 0; mask < (1u << m_domain.size()); ++mask) {
-            for (size_t i = 0; i < m_domain.size(); ++i) {
-                unsigned n = m_sizes[i] - 1;
-                unsigned left_index = min(m_inputs[i], n - 1);
-                coordinates[i] = left_index + ((mask >> i) & 1u);
-            }
+            for (size_t i = 0; i < m_domain.size(); ++i)
+                coordinates[i] = m_left_index[i] + ((mask >> i) & 1u);
             samples[mask] = sample(coordinates, r);
         }
 
         for (int i = static_cast<int>(m_domain.size() - 1); i >= 0; --i) {
-            unsigned n = m_sizes[i] - 1;
-            float ec = m_inputs[i];
-            unsigned e0 = min(static_cast<unsigned>(ec), n - 1);
             for (size_t mask = 0; mask < (1u << i); ++mask)
-                samples[mask] = mix(samples[mask], samples[mask | (1 << i)], ec - e0);
+                samples[mask] = mix(samples[mask], samples[mask | (1 << i)], m_inputs[i]);
         }
 
         float result = interpolate(samples[0], 0.0f, 255.0f, m_decode[r].lower, m_decode[r].upper);