commit fc4433ba3ca745212715bbe7b83ef8445e959ead
author Frederik van der Els <49305700+xpple@users.noreply.github.com> Tue Apr 04 23:08:58 2023 +0200
committer GitHub <noreply@github.com> Tue Apr 04 16:08:58 2023 -0500
tree 1c9be9ddc53bbe13970a34869f034a027887f96c
parent f3c2b44e35ce974d773eadbacc38e8fa1765c709

Clarify that the size of the GF is a power of two (#1612)

core/src/main/java/com/google/zxing/common/reedsolomon/GenericGF.java

diff --git a/core/src/main/java/com/google/zxing/common/reedsolomon/GenericGF.java b/core/src/main/java/com/google/zxing/common/reedsolomon/GenericGF.java
index 2b32566..3532904 100644
--- a/core/src/main/java/com/google/zxing/common/reedsolomon/GenericGF.java
+++ b/core/src/main/java/com/google/zxing/common/reedsolomon/GenericGF.java
@@ -21,20 +21,21 @@
  * the Galois Fields. Operations use a given primitive polynomial in calculations.</p>
  *
  * <p>Throughout this package, elements of the GF are represented as an {@code int}
- * for convenience and speed (but at the cost of memory).
- * </p>
+ * for convenience and speed (but at the cost of memory).</p>
+ *
+ * <p>The size of the GF is assumed to be a power of two.</p>
  *
  * @author Sean Owen
  * @author David Olivier
  */
 public final class GenericGF {
 
-  public static final GenericGF AZTEC_DATA_12 = new GenericGF(0x1069, 4096, 1); // x^12 + x^6 + x^5 + x^3 + 1
-  public static final GenericGF AZTEC_DATA_10 = new GenericGF(0x409, 1024, 1); // x^10 + x^3 + 1
-  public static final GenericGF AZTEC_DATA_6 = new GenericGF(0x43, 64, 1); // x^6 + x + 1
-  public static final GenericGF AZTEC_PARAM = new GenericGF(0x13, 16, 1); // x^4 + x + 1
-  public static final GenericGF QR_CODE_FIELD_256 = new GenericGF(0x011D, 256, 0); // x^8 + x^4 + x^3 + x^2 + 1
-  public static final GenericGF DATA_MATRIX_FIELD_256 = new GenericGF(0x012D, 256, 1); // x^8 + x^5 + x^3 + x^2 + 1
+  public static final GenericGF AZTEC_DATA_12 = new GenericGF(0b1000001101001, 4096, 1); // x^12 + x^6 + x^5 + x^3 + 1
+  public static final GenericGF AZTEC_DATA_10 = new GenericGF(0b10000001001, 1024, 1); // x^10 + x^3 + 1
+  public static final GenericGF AZTEC_DATA_6 = new GenericGF(0b1000011, 64, 1); // x^6 + x + 1
+  public static final GenericGF AZTEC_PARAM = new GenericGF(0b10011, 16, 1); // x^4 + x + 1
+  public static final GenericGF QR_CODE_FIELD_256 = new GenericGF(0b100011101, 256, 0); // x^8 + x^4 + x^3 + x^2 + 1
+  public static final GenericGF DATA_MATRIX_FIELD_256 = new GenericGF(0b100101101, 256, 1); // x^8 + x^5 + x^3 + x^2 + 1
   public static final GenericGF AZTEC_DATA_8 = DATA_MATRIX_FIELD_256;
   public static final GenericGF MAXICODE_FIELD_64 = AZTEC_DATA_6;
 
@@ -67,7 +68,7 @@
     int x = 1;
     for (int i = 0; i < size; i++) {
       expTable[i] = x;
-      x *= 2; // we're assuming the generator alpha is 2
+      x *= 2; // 2 (the polynomial x) is a primitive element
       if (x >= size) {
         x ^= primitive;
         x &= size - 1;