On Thu, 7 Apr 2022 18:23:50 GMT, Paul Sandoz <psan...@openjdk.org> wrote:
>> src/java.base/share/classes/java/lang/Integer.java line 1781: >> >>> 1779: * All the upper remaining bits of the compressed value are set >>> 1780: * to zero. >>> 1781: * >> >> Following Alan's comment, I suggest the following examples: >> >> >> compress(0x9ABCDEF, 0x0F0F0FF) == 0xACEF >> compress(x, 1<<n) == (x>>n & 1) >> compress(x, -1<<n) == x >>> n >> compress(m, m) == (m==-1||m==0)? m : (1<<bitCount(m))-1 >> compress(x, m) == compress(x & m, m) >> compress(expand(x, m), m) == x & compress(m, m) >> (compress(x, m) >>> n) & 1 == /*the bit of x corresponding to the nth set >> bit in m*/ >> >> >> …In two places. Similarly, examples for expand: >> >> >> expand(0x9ABCDEF, 0x0F0F0FF) == 0xC0D0EF >> expand(x, 1<<n) == (x&1) << n >> expand(x, -1<<n) == x << n >> expand(-1, m) == m >> expand(x, m) == expand(x, m) & m >> expand(compress(x, m), m) == x & m >> expand(1<<n, m) == /*the nth set bit in m, as a mask in place; cf. >> highest/lowestOneBit*/ >> >> >> (Please double check these examples!) > > Examples added in latest commit. I see you've added a comment on each example too, I think this really helpers readers to see how they can be used. The class description of both Integer and Long have an implementation note (they pre-date @implNote) referencing Hacker's Delight. We could potentially expand the list of methods mentioned but it's not strictly necessary are they are just examples. ------------- PR: https://git.openjdk.java.net/jdk/pull/8115
