Mercurial > octave
comparison doc/interpreter/numbers.txi @ 31069:43974344fe19 stable
doc: Expand documentation about type promotion and demotion (bug #62283)
| author | Arun Giridhar <arungiridhar@gmail.com> |
|---|---|
| date | Sat, 04 Jun 2022 17:13:38 -0400 |
| parents | 796f54d4ddbf |
| children | 2dee06f4635c |
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| 31065:d33af4594440 | 31069:43974344fe19 |
|---|---|
| 773 @end example | 773 @end example |
| 774 | 774 |
| 775 @noindent | 775 @noindent |
| 776 where the returned value is single precision. | 776 where the returned value is single precision. |
| 777 | 777 |
| 778 Many functions and operators will also promote integer or logical types to | |
| 779 double, or single to double, especially if they take only one argument. | |
| 780 | |
| 781 @example | |
| 782 @group | |
| 783 a = det (int8 ([1 2; 3 4])) | |
| 784 @result{} a = -2 | |
| 785 class (a) | |
| 786 @result{} double | |
| 787 @end group | |
| 788 @end example | |
| 789 | |
| 790 But there are also exceptions for promoting to double, especially if the | |
| 791 function or operator in question can take multiple arguments. | |
| 792 | |
| 793 @example | |
| 794 @group | |
| 795 a = eig (int8 ([1 2; 3 4])) | |
| 796 @result{} error: eig: wrong type argument 'int8 matrix' | |
| 797 @end group | |
| 798 @end example | |
| 799 | |
| 800 When the two operands are both integers but of different widths, then the | |
| 801 behavior depends on the operator or the function in question. For some | |
| 802 operators and functions, narrow-bitwidth operands are promoted to a wider | |
| 803 bitwidth: | |
| 804 | |
| 805 @example | |
| 806 @group | |
| 807 a = min (int8 (100), int16 (200)) | |
| 808 @result{} 100 | |
| 809 class (a) | |
| 810 @result{} int16 | |
| 811 @end group | |
| 812 @end example | |
| 813 | |
| 814 However, not all functions or operators will accept integer operands of | |
| 815 differing types: | |
| 816 | |
| 817 @example | |
| 818 @group | |
| 819 int8 (100) + int16 (200) | |
| 820 @result{} error: binary operator '+' not implemented | |
| 821 for 'int8 scalar' by 'int16 scalar' operations | |
| 822 @end group | |
| 823 @end example | |
| 824 | |
| 825 Further, in most cases, both operands need to be signed or both need to be | |
| 826 unsigned. Mixing signed and unsigned usually causes an error, even if they | |
| 827 are of the same bitwidth. | |
| 828 | |
| 829 @example | |
| 830 @group | |
| 831 min (int8 (100), uint16 (200)) | |
| 832 @result{} error: min: cannot compute min (int8 scalar, uint16 scalar) | |
| 833 @end group | |
| 834 @end example | |
| 835 | |
| 778 In the case of mixed type indexed assignments, the type is not | 836 In the case of mixed type indexed assignments, the type is not |
| 779 changed. For example, | 837 changed. For example, |
| 780 | 838 |
| 781 @example | 839 @example |
| 782 @group | 840 @group |