10.7 Converting poly_ints

A poly_int<n, T> can be constructed from up to n individual T coefficients, with the remaining coefficients being implicitly zero. In particular, this means that every poly_int<n, T> can be constructed from a single scalar T, or something compatible with T.

Also, a poly_int<n, T> can be constructed from a poly_int<n, U> if T can be constructed from U.

The following functions provide other forms of conversion, or test whether such a conversion would succeed.

‘value.is_constant ()’

Return true if poly_int value is a compile-time constant.

‘value.is_constant (&c1)’

Return true if poly_int value is a compile-time constant, storing it in c1 if so. c1 must be able to hold all constant values of value without loss of precision.

‘value.to_constant ()’

Assert that value is a compile-time constant and return its value. When using this function, please add a comment explaining why the condition is known to hold (for example, because an earlier phase of analysis rejected non-constants).

‘value.to_shwi (&p2)’

Return true if ‘poly_int<N, T>’ value can be represented without loss of precision as a ‘poly_int<N, HOST_WIDE_INT>’, storing it in that form in p2 if so.

‘value.to_uhwi (&p2)’

Return true if ‘poly_int<N, T>’ value can be represented without loss of precision as a ‘poly_int<N, unsigned HOST_WIDE_INT>’, storing it in that form in p2 if so.

‘value.force_shwi ()’

Forcibly convert each coefficient of ‘poly_int<N, T>’ value to HOST_WIDE_INT, truncating any that are out of range. Return the result as a ‘poly_int<N, HOST_WIDE_INT>’.

‘value.force_uhwi ()’

Forcibly convert each coefficient of ‘poly_int<N, T>’ value to unsigned HOST_WIDE_INT, truncating any that are out of range. Return the result as a ‘poly_int<N, unsigned HOST_WIDE_INT>’.

‘wi::shwi (value, precision)’

Return a poly_int with the same value as value, but with the coefficients converted from HOST_WIDE_INT to wide_int. precision specifies the precision of the wide_int cofficients; if this is wider than a HOST_WIDE_INT, the coefficients of value will be sign-extended to fit.

‘wi::uhwi (value, precision)’

Like wi::shwi, except that value has coefficients of type unsigned HOST_WIDE_INT. If precision is wider than a HOST_WIDE_INT, the coefficients of value will be zero-extended to fit.

‘wi::sext (value, precision)’

Return a poly_int of the same type as value, sign-extending every coefficient from the low precision bits. This in effect applies wi::sext to each coefficient individually.

‘wi::zext (value, precision)’

Like wi::sext, but for zero extension.

‘poly_wide_int::from (value, precision, sign)’

Convert value to a poly_wide_int in which each coefficient has precision bits. Extend the coefficients according to sign if the coefficients have fewer bits.

‘poly_offset_int::from (value, sign)’

Convert value to a poly_offset_int, extending its coefficients according to sign if they have fewer bits than offset_int.

‘poly_widest_int::from (value, sign)’

Convert value to a poly_widest_int, extending its coefficients according to sign if they have fewer bits than widest_int.