I have changed the float size from 32-bits to 64-bit, the measure result is nearly unchanged(from 900ms to 912ms).
result of 32-bits
best value is 0.00000000005988138 and best x is 0.0003912286
best value is 0.0000000000035196058 and best x is 0.00015211242
best value is 0.00000000057644883 and best x is 0.0008322496
best value is 0.000000000008696707 and best x is 0.00020564506
best value is 0.0000000000067636847 and best x is 0.00018911579
best value is 0.0000000010156723 and best x is 0.0010051971
best value is 0.000000000000001479852 and best x is 0.0000113956585
best value is 0.00000000046494394 and best x is 0.00077469996
best value is 0.000000000012882024 and best x is 0.00023442002
best value is 0.0000000021282005 and best x is 0.0012862859
mean time is 900ms
result of 64-bits
best value is 0.0000000058477668720127 and best x is 0.00180162064657216
best value is 0.0000000000026611724419478304 and best x is 0.00013857695232211142
best value is 0.00000000058150870335642 and best x is 0.0008346775636545467
best value is 0.000000000478984608281727 and best x is 0.0007824210378905012
best value is 0.000000000049074388830549084 and best x is 0.00036611565524501843
best value is 0.0000000005200740879052685 and best x is 0.0008041833405643376
best value is 0.00000000016031596668945342 and best x is 0.0005432406489841435
best value is 0.000000000048342858468375267 and best x is 0.00036428736532565057
best value is 0.0000000027258092748919238 and best x is 0.0013968994777376063
best value is 0.000000002512357508542904 and best x is 0.0013594413630785727
mean time is 912ms