Add accuracy document

spec/design_topics/accuracy.md

@@ -0,0 +1,56 @@
+.. _accuracy:
+
+# Accuracy
+
+## Arithmetic Operations
+
+The results of element-wise arithmetic operations
+
+-   `+`
+-   `-`
+-   `*`
+-   `/`
+-   `%`
+
+including the corresponding element-wise array APIs defined in this standard
+
+-   add
+-   subtract
+-   multiply
+-   divide
+
+for floating-point operands must return the nearest representable value according to IEEE 754-2019 and a supported rounding mode. By default, the rounding mode should be `roundTiesToEven` (i.e., ties rounded toward the nearest value with an even least significant bit).
+
+## Mathematical Functions
+
+This specification does **not** precisely define the behavior of the following functions
+
+-   acos
+-   acosh
+-   asin
+-   asinh
+-   atan
+-   atanh
+-   cos
+-   cosh
+-   exp
+-   log
+-   sin
+-   sinh
+-   sqrt
+-   tan
+-   tanh
+
+except to require specific results for certain argument values that represent boundary cases of interest.
+
+For other argument values, these functions should compute approximations to the results of respective mathematical functions; however, this specification recognizes that array libraries may be constrained by underlying hardware and/or seek to optimize performance over absolute accuracy and, thus, allows some latitude in the choice of approximation algorithms.
+
+Although the specification leaves the choice of algorithms to the implementation, this specification recommends (but does not specify) that implementations use the approximation algorithms for IEEE 754-2019 arithmetic contained in [fdlibm](http://www.netlib.org/fdlibm), the freely distributable mathematical library from Sun Microsystems, or some other comparable IEEE 754-2019 compliant mathematical library.
+
+## Statistical Functions
+
+(TODO)
+
+## Linear Algebra
+
+(TODO)

spec/design_topics/index.rst

@@ -12,5 +12,6 @@ Design topics & constraints
    array_ducktyping
    data_interchange
    missing_data
+   accuracy
    portability
    C_API