Yes,

test1:  0  differences
test2:  51  differences
test3:  0  differences

 Oddly, the relative error is always the same:

98 z different 2.0494565872e-16
99 z different 2.0494565872e-16

Which is nearly the same as the double precision 2.2204460492503131e-16, the difference being due to the fact that the precision is defined relative to 1, and the error in the computation are in a number relatively larger (more bits set, but not yet 2).

So this looks like an error in the LSB of the floating number. Could be rounding, could be something not reset quite right. I'm thinking possibly hardware at this time, maybe compiler.

Linux fedora 2.6.19-1.2895.fc6 #1 SMP Wed Jan 10 19:28:18 EST 2007 i686 athlon i386 GNU/Linux

processor       : 0
vendor_id       : AuthenticAMD
cpu family      : 15
model           : 12
model name      : AMD Athlon(tm) 64 Processor 2800+
stepping        : 0
cpu MHz         : 1808.786
cache size      : 512 KB
fdiv_bug        : no
hlt_bug         : no
f00f_bug        : no
coma_bug        : no
fpu             : yes
fpu_exception   : yes
cpuid level     : 1
wp              : yes
flags           : fpu vme de pse tsc msr pae mce cx8 apic mtrr pge mca cmov pat pse36 clflush mmx fxsr sse sse2 syscall nx mmxext lm 3dnowext 3dnow up ts fid vid ttp
bogomips        : 3618.83
Athlon 64 running 32 bit linux.

Chuck