ios - NSNumbers with value 0.5 and 1.0 have the same hash -

ios - NSNumbers with value 0.5 and 1.0 have the same hash -

can please confirm, , explain, why happens:

on simulator (7.1, 32-bit):

nsnumber *a = [nsnumber numberwithfloat:0.5]; // hash = 506952114 nsnumber *b = [nsnumber numberwithfloat:1.0]; // hash = 2654435761 nsnumber *c = [nsnumber numberwithfloat:2.0]; // hash = 1013904226

on device (7.1, 32-bit):

nsnumber *a = [nsnumber numberwithfloat:0.5]; // hash = 2654435761 nsnumber *b = [nsnumber numberwithfloat:1.0]; // hash = 2654435761 - same! nsnumber *c = [nsnumber numberwithfloat:2.0]; // hash = 5308871522

i thought might 32-bit issue, when seek same thing on 64-bit simulator , device, same issue. simulator fine, device has identical hashes.

i trying add together unique objects nsmutableorderedset , noticed 2 objects identical except differing values of 0.5 , 1.0 not both beingness added, , why. tried both floats , doubles same result.

but why?

i think excellent article mike ash might give insight:

for floats integer values, want same thing. since our isequal: considers integer-valued double equal int or uint of same value, must homecoming same hash int , uint equivalent. accomplish this, check see if double value integer, , homecoming integer value if so:

if(_value.d == floor(_value.d)) homecoming [self unsignedintegervalue];

(i won't quote whole section hash, please read article total disclosure).

but, bottom line, looks using [nsnumber hash] bad thought key in associative array/hash table. cannot explain why behaves differently under simulator , device; looks troubling...

ios objective-c nsnumber