Handle non-integer and out-of-range values correctly in Indexed color spaces

In PDF version 2.0 the handling of Indexed color spaces was clarified as follows:
> The index value should be an integer in the range 0 to hival. If the value is a real number, it shall be rounded to the nearest integer (0.5 values shall be rounded up); if it is outside the range 0 to hival, it shall be adjusted to the nearest value within that range.

Please refer to https://github.com/pdf-association/pdf-differences/tree/main/IndexedColor

Author: Snuffleupagus

src/core/colorspace.js

@@ -429,6 +429,7 @@ class IndexedCS extends ColorSpace {
   constructor(base, highVal, lookup) {
     super("Indexed", 1);
     this.base = base;
+    this.highVal = highVal;
 
     const length = base.numComps * (highVal + 1);
     this.lookup = new Uint8Array(length);
@@ -452,9 +453,10 @@ class IndexedCS extends ColorSpace {
         'IndexedCS.getRgbItem: Unsupported "dest" type.'
       );
     }
-    const numComps = this.base.numComps;
-    const start = src[srcOffset] * numComps;
-    this.base.getRgbBuffer(this.lookup, start, 1, dest, destOffset, 8, 0);
+    const { base, highVal, lookup } = this;
+    const start =
+      MathClamp(Math.round(src[srcOffset]), 0, highVal) * base.numComps;
+    base.getRgbBuffer(lookup, start, 1, dest, destOffset, 8, 0);
   }
 
   getRgbBuffer(src, srcOffset, count, dest, destOffset, bits, alpha01) {
@@ -464,13 +466,13 @@ class IndexedCS extends ColorSpace {
         'IndexedCS.getRgbBuffer: Unsupported "dest" type.'
       );
     }
-    const base = this.base;
-    const numComps = base.numComps;
+    const { base, highVal, lookup } = this;
+    const { numComps } = base;
     const outputDelta = base.getOutputLength(numComps, alpha01);
-    const lookup = this.lookup;
 
     for (let i = 0; i < count; ++i) {
-      const lookupPos = src[srcOffset++] * numComps;
+      const lookupPos =
+        MathClamp(Math.round(src[srcOffset++]), 0, highVal) * numComps;
       base.getRgbBuffer(lookup, lookupPos, 1, dest, destOffset, 8, alpha01);
       destOffset += outputDelta;
     }

test/pdfs/.gitignore

@@ -191,6 +191,7 @@
 !rotation.pdf
 !simpletype3font.pdf
 !Type3WordSpacing.pdf
+!IndexedCS_negative_and_high.pdf
 !sizes.pdf
 !javauninstall-7r.pdf
 !file_url_link.pdf

test/pdfs/IndexedCS_negative_and_high.pdf

@@ -2851,6 +2851,14 @@
     "rounds": 1,
     "type": "eq"
   },
+  {
+    "id": "IndexedCS_negative_and_high",
+    "file": "pdfs/IndexedCS_negative_and_high.pdf",
+    "md5": "3bbf5e6f1cf49acb075fabb0726b5fe4",
+    "link": false,
+    "rounds": 1,
+    "type": "eq"
+  },
   {
     "id": "issue13372",
     "file": "pdfs/issue13372.pdf",