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ICU-8915 document why BMPSet.set32x64Bits(..., limit=0x800) is fine & safe

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X-SVN-Rev: 31001
This commit is contained in:
Markus Scherer 2011-12-01 06:47:04 +00:00
parent 540221ad33
commit 77b94f2bd1
1 changed files with 6 additions and 2 deletions
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8
icu4j/main/classes/core/src/com/ibm/icu/impl/BMPSet.java
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@ -316,8 +316,8 @@ public final class BMPSet {
*/
private static void set32x64Bits(int[] table, int start, int limit) {
assert (64 == table.length);
int lead = start >> 6;
int trail = start & 0x3f;
int lead = start >> 6; // Named for UTF-8 2-byte lead byte with upper 5 bits.
int trail = start & 0x3f; // Named for UTF-8 2-byte trail byte with lower 6 bits.
// Set one bit indicating an all-one block.
int bits = 1 << lead;
@ -353,6 +353,10 @@ public final class BMPSet {
table[trail] |= bits;
}
}
// limit<=0x800. If limit==0x800 then limitLead=32 and limitTrail=0.
// In that case, bits=1<<limitLead == 1<<0 == 1
// (because Java << uses only the lower 5 bits of the shift operand)
// but the bits value is not used because trail<limitTrail is already false.
bits = 1 << limitLead;
for (trail = 0; trail < limitTrail; ++trail) {
table[trail] |= bits;