Apple's code does:
int *dest ... ; for (i = count; i > 0; i -= 4) *dest++ = value;
Oh, and it does an unsigned 32-bit read for the (signed) count; this means that on 64-bit systems it does not work for negative count values. Not that it is ever called like that, heh.
Here's the code if you care (from 5.2.4f1, i.e. for G5 machines):
58c0: 7e 84 a3 78 mr r4,r20 58c4: 80 7f 00 00 lwz r3,0(r31) 58c8: 80 bf 00 04 lwz r5,4(r31) 58cc: 7c 63 1b 79 mr. r3,r3 58d0: 86 9f 00 08 lwzu r20,8(r31) 58d4: 3b ff 00 04 addi r31,r31,4 58d8: 40 81 00 14 ble 0x58ec 58dc: 34 63 ff fc addic. r3,r3,-4 58e0: 90 85 00 00 stw r4,0(r5) 58e4: 38 a5 00 04 addi r5,r5,4 58e8: 42 80 ff f0 bc 20,lt,0x58d8 58ec: 4e 80 00 20 blr
Segher