FN-TRUNC-001: TRUNC of DBL_MIN returns a subnormal, not 0
Excel differs from the mathematical answer · measured · recorded 2026-11-04
With DBL_MIN (0x0010000000000000) as number, TRUNC, ROUNDDOWN and ROUNDUP return the subnormal 0x000ffffffffffffa at each num_digits recorded, so TRUNC(DBL_MIN,0) is not 0. That value is 6 steps below DBL_MIN and 3 steps below 0x000ffffffffffffd, the binary64 nearest the 15-digit reading 2.22507385850720E-308. The recorded rows hold 256 such cases for each of the three functions. ROUND gives 0 on the same inputs.
| Call and input route | Inputs | Excel | Correct value | Recorded in |
|---|---|---|---|---|
TRUNC(2.2250738585072014e-308, 0)cell-value2 | number: 2.2250738585072014e-3080x0010000000000000num_digits: 00x0000000000000000 | 2.2250738585071984e-3080x000ffffffffffffa | 00x0000000000000000 | Excel 16.0 build 20430, Windows 64-bit, CPU not recorded in this capture |
TRUNC(2.2250738585072014e-308, 1)cell-value2 | number: 2.2250738585072014e-3080x0010000000000000num_digits: 10x3ff0000000000000 | 2.2250738585071984e-3080x000ffffffffffffa | 00x0000000000000000 | Excel 16.0 build 20430, Windows 64-bit, CPU not recorded in this capture |
Correct value: DBL_MIN is below 1, so truncating it at 0 or 1 places gives 0.
Correct value: DBL_MIN is below 1, so truncating it at 0 or 1 places gives 0.
Basis: Recorded rows of the broad capture; counts from the rounding write-up.
Open: Why this one input converts 3 steps below nearest.
Evidence and capture sources
- ExcelFunctionsHandbook · content/notes/evidence/2026-11-04/rounding-EVIDENCE.md b5d84a80a5a4640eca9ce04f232c0bc115503f34 · research write-up: full-bank result, the rules, what stays open
- CalcFunc-Evidence · runs/w111-broad-20260929/answers/answers-trunc.json.gz 4d5320dfdc385354469b4d506153357bb932ab08 · w111broad-20260929-TRUNC-00026
- CalcFunc-Evidence · runs/w111-broad-20260929/answers/answers-trunc.json.gz 4d5320dfdc385354469b4d506153357bb932ab08 · w111broad-20260929-TRUNC-00027