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### 598. [dec.tr] Conversion to integral should truncate, not round.

**Section:** 3.2 [dec.tr::trdec.types.types] **Status:** TRDec
**Submitter:** Daniel Krugler **Opened:** 2006-05-28 **Last modified:** 2017-02-03

**Priority: **Not Prioritized

**View all other** issues in [dec.tr::trdec.types.types].

**View all issues with** TRDec status.

**Discussion:**

In a private email, Daniel writes:

I would like to
ask, what where the reason for the decision to
define the semantics of the integral conversion of the decimal types, namely

"operator long long() const;
Returns: Returns the result of the
conversion of *this to the type long long, as if
performed by the expression llrounddXX(*this)."

where XX stands for either 32, 64, or 128,
corresponding to the proper decimal type. The
exact meaning of llrounddXX is not given in that
paper, so I compared it to the corresponding
definition given in C99, 2nd edition (ISO 9899), which says in 7.12.9.7 p. 2:

"The lround and llround functions round their
argument to the nearest integer value,
rounding halfway cases away from zero, regardless
of the current rounding direction. [..]"

Now considering the fact that integral conversion
of the usual floating-point types ("4.9
Floating-integral conversions") has truncation
semantic I wonder why this conversion behaviour
has not been transferred for the decimal types.

Robert comments:

Also, there is a further error in the **Returns:** clause for converting `decimal::decimal128`

to `long long`

. It currently calls `llroundd64`

, not `llroundd128`

.

**Proposed resolution:**

Change the **Returns:** clause in 3.2.2.4 to:

**Returns:** Returns the result of the conversion of `*this`

to the type `long long`

, as if performed by the expression `llroundd32(*this)`

while the decimal rounding direction mode [3.5.2] `FE_DEC_TOWARD_ZERO`

is in effect.

Change the **Returns:** clause in 3.2.3.4 to:

**Returns:** Returns the result of the conversion of `*this`

to the type `long long`

, as if performed by the expression `llroundd64(*this)`

while the decimal rounding direction mode [3.5.2] `FE_DEC_TOWARD_ZERO`

is in effect.

Change the **Returns:** clause in 3.2.4.4 to:

**Returns:** Returns the result of the conversion of `*this`

to the type `long long`

, as if performed by the expression `llroundd64(*this)`

`llroundd128(*this)`

while the decimal rounding direction mode [3.5.2] `FE_DEC_TOWARD_ZERO`

is in effect.