yaml_test: adapt around undefined behavior in float64->int64 casting

[neolit123]

In TestJSONObjectToYAMLObject the "uint64 big" case accepts a float64
of size 2^63. The value is passed to jsonToYAMLValue() and the
float64 branch of the switch is entered. For values that do not
fit int64 the first cast to int64() is undefined behavior
in most languages and apparently in Golang:
http://c0x.coding-guidelines.com/6.3.1.4.pdf
(link for the C standard)

This means the value of int64(float64(2^63)) can end up as either
-9223372036854775808 or 9223372036854775807.
From experimentation, it appears compiler optimization
determines the result.

The value is then casted back to float64 and matched against
the original float64, which may or may not pass. Depending of FPU
rounding mode for IEEE754-Doubles any input above 9223372036854775296
may get casted to 9223372036854775808.0.

Adapt the unit test for "uint64 big" to not feed a big float64 and enter
the problem cases. Instead pass the nearest rounded value of 2^63
as a uint64 and expect to receive the same result:
bigUint64 = ((uint64(1) << 63) + 500) / 1000 * 1000

the observed undefined behavior seems to trip tests on non-AMD64:
fixes #34

[neolit123]

while jsonToYAMLValue is doing something that is not recommended, it appears to match existing logic in https://github.com/go-yaml/yaml, so i left it untouched.

/kind bug
/sig api-machinery
/priority backlog
/cc @sttts

[dims]

tested this on a real arm64 box:

[ubuntu@ip-172-31-41-104 23:44] ~/go/src/sigs.k8s.io/yaml ⟩ uname -a
Linux ip-172-31-41-104 5.4.0-1035-aws #37-Ubuntu SMP Wed Jan 6 21:02:01 UTC 2021 aarch64 aarch64 aarch64 GNU/Linux

[dims]

cpu info

[ubuntu@ip-172-31-41-104 23:46] ~/go/src/sigs.k8s.io/yaml ⟩ lscpu
Architecture:                    aarch64
CPU op-mode(s):                  32-bit, 64-bit
Byte Order:                      Little Endian
CPU(s):                          8
On-line CPU(s) list:             0-7
Thread(s) per core:              1
Core(s) per socket:              8
Socket(s):                       1
NUMA node(s):                    1
Vendor ID:                       ARM
Model:                           1
Model name:                      Neoverse-N1
Stepping:                        r3p1
BogoMIPS:                        243.75
L1d cache:                       512 KiB
L1i cache:                       512 KiB
L2 cache:                        8 MiB
L3 cache:                        32 MiB
NUMA node0 CPU(s):               0-7
Vulnerability Itlb multihit:     Not affected
Vulnerability L1tf:              Not affected
Vulnerability Mds:               Not affected
Vulnerability Meltdown:          Not affected
Vulnerability Spec store bypass: Mitigation; Speculative Store Bypass disabled via prctl
Vulnerability Spectre v1:        Mitigation; __user pointer sanitization
Vulnerability Spectre v2:        Not affected
Vulnerability Srbds:             Not affected
Vulnerability Tsx async abort:   Not affected
Flags:                           fp asimd evtstrm aes pmull sha1 sha2 crc32 atomics fphp asimdhp cpuid asimdrdm lrcpc dcpop asimdd
                                 p ssbs

[dims]

/approve
/lgtm

[k8s-ci-robot]

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