Delphi's Round() appears to be non-deterministic

user_1163893 0
Viewed 184

I'm facing the bizarre situation that the same program on the same machine doing a Round() of the same floating point value does not always give the same result. At first I thought it has to be glitch because of a bit flip or something, but it keeps on coming back. Now it started to happen on a completely different machine as well. Bad results come up rather rarely, in the order of once a week. When they do, it seems they keep happening until the program is restarted. That might be a coincidence, however. So far, I've been unable to reproduce it at will. This is all happening on the main thread, by the way.

A check I consider adding is whether Round keeps pointing to the same memory address. Any other ideas?

2020-12-28 08:30:19.411 DBGrid1.Fields[17].AsString: 0,239999994635582
2020-12-28 08:30:19.411 FloatToStr(DBGrid1.Fields[17].AsFloat): 0,239999994635582
2020-12-28 08:30:19.411 FloatToStr(1000 * DBGrid1.Fields[17].AsFloat): 239,999994635582
2020-12-28 08:30:19.411 IntToStr(Round(1000 * DBGrid1.Fields[17].AsFloat)): 239
2020-12-28 08:30:19.411 FloatToStr(DBGrid1.Fields[17].AsSingle): 0,239999994635582
2020-12-28 08:30:19.411 FloatToStr(1000 * DBGrid1.Fields[17].AsSingle): 239,999994635582
2020-12-28 08:30:19.411 IntToStr(Round(1000 * DBGrid1.Fields[17].AsSingle)): 239
2020-12-28 08:30:19.411 FloatToStr(DBGrid1.Fields[17].AsExtended): 0,239999994635582
2020-12-28 08:30:19.412 FloatToStr(1000 * DBGrid1.Fields[17].AsExtended): 239,999994635582
2020-12-28 08:30:19.412 IntToStr(Round(1000 * DBGrid1.Fields[17].AsExtended)): 239
2020-12-28 08:30:19.412 CurrToStr(DBGrid1.Fields[17].AsCurrency): 0,2399
2020-12-28 08:30:19.412 CurrToStr(1000 * DBGrid1.Fields[17].AsCurrency): 239,9
2020-12-28 08:30:19.412 IntToStr(Round(1000 * DBGrid1.Fields[17].AsCurrency)): 239
2020-12-28 08:30:19.412 FloatToStr(Query1.FieldByName('FIELD').AsFloat): 0,239999994635582
2020-12-28 08:30:19.412 FloatToStr(1000 * Query1.FieldByName('FIELD').AsFloat): 239,999994635582
2020-12-28 08:30:19.412 IntToStr(Round(1000 * Query1.FieldByName('FIELD').AsFloat)): 239
2020-12-28 08:30:19.412 FloatToStr(Query1.FieldByName('FIELD').AsSingle): 0,239999994635582
2020-12-28 08:30:19.412 FloatToStr(1000 * Query1.FieldByName('FIELD').AsSingle): 239,999994635582
2020-12-28 08:30:19.413 IntToStr(Round(1000 * Query1.FieldByName('FIELD').AsSingle)): 239
2020-12-28 08:30:19.413 FloatToStr(Query1.FieldByName('FIELD').AsExtended): 0,239999994635582
2020-12-28 08:30:19.413 FloatToStr(1000 * Query1.FieldByName('FIELD').AsExtended): 239,999994635582
2020-12-28 08:30:19.413 IntToStr(Round(1000 * Query1.FieldByName('FIELD').AsExtended)): 239
2020-12-28 08:30:19.413 CurrToStr(Query1.FieldByName('FIELD').AsCurrency): 0,2399
2020-12-28 08:30:19.413 CurrToStr(1000 * Query1.FieldByName('FIELD').AsCurrency): 239,9
2020-12-28 08:30:19.413 IntToStr(Round(1000 * Query1.FieldByName('FIELD').AsCurrency)): 239
2020-12-28 08:30:19.413 CurrToStr(Query1.FieldByName('FIELD').AsCurrency): 0,2399
2020-12-28 08:30:19.413 CurrToStr(1000 * Query1.FieldByName('FIELD').AsCurrency): 239,9
2020-12-28 08:30:19.413 IntToStr(Round(1000 * Query1.FieldByName('FIELD').AsCurrency)): 239
2020-12-28 08:30:19.414 BinToHex(DBGrid1.Fields[17].AsFloat): 00000000008FC2F5FC3F

2020-12-28 08:40:46.461 DBGrid1.Fields[17].AsString: 0,239999994635582
2020-12-28 08:40:46.462 FloatToStr(DBGrid1.Fields[17].AsFloat): 0,239999994635582
2020-12-28 08:40:46.463 FloatToStr(1000 * DBGrid1.Fields[17].AsFloat): 239,999994635582
2020-12-28 08:40:46.463 IntToStr(Round(1000 * DBGrid1.Fields[17].AsFloat)): 240
2020-12-28 08:40:46.463 FloatToStr(DBGrid1.Fields[17].AsSingle): 0,239999994635582
2020-12-28 08:40:46.463 FloatToStr(1000 * DBGrid1.Fields[17].AsSingle): 239,999994635582
2020-12-28 08:40:46.463 IntToStr(Round(1000 * DBGrid1.Fields[17].AsSingle)): 240
2020-12-28 08:40:46.463 FloatToStr(DBGrid1.Fields[17].AsExtended): 0,239999994635582
2020-12-28 08:40:46.463 FloatToStr(1000 * DBGrid1.Fields[17].AsExtended): 239,999994635582
2020-12-28 08:40:46.463 IntToStr(Round(1000 * DBGrid1.Fields[17].AsExtended)): 240
2020-12-28 08:40:46.463 CurrToStr(DBGrid1.Fields[17].AsCurrency): 0,24
2020-12-28 08:40:46.463 CurrToStr(1000 * DBGrid1.Fields[17].AsCurrency): 240
2020-12-28 08:40:46.463 IntToStr(Round(1000 * DBGrid1.Fields[17].AsCurrency)): 240
2020-12-28 08:40:46.463 FloatToStr(Query1.FieldByName('FIELD').AsFloat): 0,239999994635582
2020-12-28 08:40:46.463 FloatToStr(1000 * Query1.FieldByName('FIELD').AsFloat): 239,999994635582
2020-12-28 08:40:46.463 IntToStr(Round(1000 * Query1.FieldByName('FIELD').AsFloat)): 240
2020-12-28 08:40:46.463 FloatToStr(Query1.FieldByName('FIELD').AsSingle): 0,239999994635582
2020-12-28 08:40:46.464 FloatToStr(1000 * Query1.FieldByName('FIELD').AsSingle): 239,999994635582
2020-12-28 08:40:46.464 IntToStr(Round(1000 * Query1.FieldByName('FIELD').AsSingle)): 240
2020-12-28 08:40:46.464 FloatToStr(Query1.FieldByName('FIELD').AsExtended): 0,239999994635582
2020-12-28 08:40:46.464 FloatToStr(1000 * Query1.FieldByName('FIELD').AsExtended): 239,999994635582
2020-12-28 08:40:46.464 IntToStr(Round(1000 * Query1.FieldByName('FIELD').AsExtended)): 240
2020-12-28 08:40:46.464 CurrToStr(Query1.FieldByName('FIELD').AsCurrency): 0,24
2020-12-28 08:40:46.464 CurrToStr(1000 * Query1.FieldByName('FIELD').AsCurrency): 240
2020-12-28 08:40:46.464 IntToStr(Round(1000 * Query1.FieldByName('FIELD').AsCurrency)): 240
2020-12-28 08:40:46.464 CurrToStr(Query1.FieldByName('FIELD').AsCurrency): 0,24
2020-12-28 08:40:46.464 CurrToStr(1000 * Query1.FieldByName('FIELD').AsCurrency): 240
2020-12-28 08:40:46.465 IntToStr(Round(1000 * Query1.FieldByName('FIELD').AsCurrency)): 240
2020-12-28 08:40:46.465 BinToHex(DBGrid1.Fields[17].AsFloat): 00000000008FC2F5FC3F
x87 delphi-2010 floating-point rounding delphi
1 Answers

Round is deterministic. However, its behaviour depends on the prevailing floating point rounding mode, as well as its argument. Something else in your program is changing the rounding mode.

user_5050880
Related