update snappy.cc Optimize by about 7.82%

[MacChen02]

Replacing functions with macros to improve performance. snappy_unittest Optimize by about 7.82%.
name old speed new speed improve
BM_UFlat/0 324.8 319.8 -1.54%
BM_UFlat/1 291.6 289.5 -0.72%
BM_UFlat/2 17.4 17.5 0.57%
BM_UFlat/3 290.4 299.3 3.06%
BM_UFlat/4 2.6 2.6 0.00%
BM_UFlat/5 416.5 410.3 -1.49%
BM_UFlat/6 125.7 159.4 26.81%
BM_UFlat/7 153.8 151.7 -1.37%
BM_UFlat/8 173.1 170.6 -1.44%
BM_UFlat/9 143.1 141.4 -1.19%
BM_UFlat/10 406.3 523.1 28.75%
BM_UFlat/11 188.6 184.7 -2.07%
BM_UIOVec/0 293.3 305.9 4.30%
BM_UIOVec/1 226.6 232.6 2.65%
BM_UIOVec/2 20.5 20.8 1.46%
BM_UIOVec/3 204.5 204 -0.24%
BM_UIOVec/4 2.7 2.9 7.41%
BM_UValidate/0 873 874.1 0.13%
BM_UValidate/1 537.1 536.1 -0.19%
BM_UValidate/2 231.2 229.1 -0.91%
BM_UValidate/3 592.7 577.2 -2.62%
BM_UValidate/4 9 9 0.00%
BM_ZFlat/0 161.9 181.2 11.92%
BM_ZFlat/1 85.5 100.7 17.78%
BM_ZFlat/2 5.6 7.2 28.57%
BM_ZFlat/3 71.4 95.1 33.19%
BM_ZFlat/4 1.5 1.7 13.33%
BM_ZFlat/5 159.8 179.2 12.14%
BM_ZFlat/6 61.1 68.3 11.78%
BM_ZFlat/7 58.1 65.2 12.22%
BM_ZFlat/8 64.6 72.2 11.76%
BM_ZFlat/9 54.8 61.5 12.23%
BM_ZFlat/10 203.3 230.1 13.18%
BM_ZFlat/11 90.2 97.7 8.31%
BM_ZFlatAll/0 85.5 96.7 13.10%
BM_ZFlatIncreasingTableSize/0 94.9 114.5 20.65%

AVG : 7.82%

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[MacChen02]

@googlebot I signed it!

[MacChen02]

@googlebot I signed it!

[MacChen02]

@googlebot I signed it!

[MacChen02]

@googlebot I signed it, please help to confirm it, thks.

[MacChen02]

@pwnall @googlebot I signed it. Please help to confirm it, or what other problem? thks.