1 // © 2017 and later: Unicode, Inc. and others.
2 // License & terms of use: http://www.unicode.org/copyright.html
3 
4 #include "unicode/utypes.h"
5 
6 #if !UCONFIG_NO_FORMATTING && !UPRV_INCOMPLETE_CPP11_SUPPORT
7 #ifndef __NUMBER_ROUNDINGUTILS_H__
8 #define __NUMBER_ROUNDINGUTILS_H__
9 
10 #include "number_types.h"
11 
12 U_NAMESPACE_BEGIN
13 namespace number {
14 namespace impl {
15 namespace roundingutils {
16 
17 enum Section {
18     SECTION_LOWER_EDGE = -1,
19     SECTION_UPPER_EDGE = -2,
20     SECTION_LOWER = 1,
21     SECTION_MIDPOINT = 2,
22     SECTION_UPPER = 3
23 };
24 
25 /**
26  * Converts a rounding mode and metadata about the quantity being rounded to a boolean determining
27  * whether the value should be rounded toward infinity or toward zero.
28  *
29  * <p>The parameters are of type int because benchmarks on an x86-64 processor against OpenJDK
30  * showed that ints were demonstrably faster than enums in switch statements.
31  *
32  * @param isEven Whether the digit immediately before the rounding magnitude is even.
33  * @param isNegative Whether the quantity is negative.
34  * @param section Whether the part of the quantity to the right of the rounding magnitude is
35  *     exactly halfway between two digits, whether it is in the lower part (closer to zero), or
36  *     whether it is in the upper part (closer to infinity). See {@link #SECTION_LOWER}, {@link
37  *     #SECTION_MIDPOINT}, and {@link #SECTION_UPPER}.
38  * @param roundingMode The integer version of the {@link RoundingMode}, which you can get via
39  *     {@link RoundingMode#ordinal}.
40  * @param status Error code, set to U_FORMAT_INEXACT_ERROR if the rounding mode is kRoundUnnecessary.
41  * @return true if the number should be rounded toward zero; false if it should be rounded toward
42  *     infinity.
43  */
44 inline bool
45 getRoundingDirection(bool isEven, bool isNegative, Section section, RoundingMode roundingMode,
46                      UErrorCode &status) {
47     switch (roundingMode) {
48         case RoundingMode::UNUM_ROUND_UP:
49             // round away from zero
50             return false;
51 
52         case RoundingMode::UNUM_ROUND_DOWN:
53             // round toward zero
54             return true;
55 
56         case RoundingMode::UNUM_ROUND_CEILING:
57             // round toward positive infinity
58             return isNegative;
59 
60         case RoundingMode::UNUM_ROUND_FLOOR:
61             // round toward negative infinity
62             return !isNegative;
63 
64         case RoundingMode::UNUM_ROUND_HALFUP:
65             switch (section) {
66                 case SECTION_MIDPOINT:
67                     return false;
68                 case SECTION_LOWER:
69                     return true;
70                 case SECTION_UPPER:
71                     return false;
72                 default:
73                     break;
74             }
75             break;
76 
77         case RoundingMode::UNUM_ROUND_HALFDOWN:
78             switch (section) {
79                 case SECTION_MIDPOINT:
80                     return true;
81                 case SECTION_LOWER:
82                     return true;
83                 case SECTION_UPPER:
84                     return false;
85                 default:
86                     break;
87             }
88             break;
89 
90         case RoundingMode::UNUM_ROUND_HALFEVEN:
91             switch (section) {
92                 case SECTION_MIDPOINT:
93                     return isEven;
94                 case SECTION_LOWER:
95                     return true;
96                 case SECTION_UPPER:
97                     return false;
98                 default:
99                     break;
100             }
101             break;
102 
103         default:
104             break;
105     }
106 
107     status = U_FORMAT_INEXACT_ERROR;
108     return false;
109 }
110 
111 /**
112  * Gets whether the given rounding mode's rounding boundary is at the midpoint. The rounding
113  * boundary is the point at which a number switches from being rounded down to being rounded up.
114  * For example, with rounding mode HALF_EVEN, HALF_UP, or HALF_DOWN, the rounding boundary is at
115  * the midpoint, and this function would return true. However, for UP, DOWN, CEILING, and FLOOR,
116  * the rounding boundary is at the "edge", and this function would return false.
117  *
118  * @param roundingMode The integer version of the {@link RoundingMode}.
119  * @return true if rounding mode is HALF_EVEN, HALF_UP, or HALF_DOWN; false otherwise.
120  */
121 inline bool roundsAtMidpoint(int roundingMode) {
122     switch (roundingMode) {
123         case RoundingMode::UNUM_ROUND_UP:
124         case RoundingMode::UNUM_ROUND_DOWN:
125         case RoundingMode::UNUM_ROUND_CEILING:
126         case RoundingMode::UNUM_ROUND_FLOOR:
127             return false;
128 
129         default:
130             return true;
131     }
132 }
133 
134 } // namespace roundingutils
135 } // namespace impl
136 } // namespace number
137 U_NAMESPACE_END
138 
139 #endif //__NUMBER_ROUNDINGUTILS_H__
140 
141 #endif /* #if !UCONFIG_NO_FORMATTING */
142