dashu-macros 0.6.0

Procedural macros for the dashu math types: create big-number literals at compile time with ubig!, ibig!, fbig!, dbig!, rbig!, and cbig! (plus their static_ variants for const contexts). Each literal follows the same parsing rules as the corresponding dashu type, producing values of UBig, IBig, FBig, RBig, or CBig in any supported base.
Documentation 
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use dashu_base::{BitTest, ParseError};
use dashu_int::{IBig, Sign, UBig};
use proc_macro2::{TokenStream, TokenTree};
use quote::quote;

use super::common::{quote_bytes, quote_sign, quote_words, unwrap_with_error_msg};

pub fn parse_integer(
    signed: bool,
    static_: bool,
    embedded: bool,
    input: TokenStream,
) -> TokenStream {
    let (sign, big) = unwrap_with_error_msg(parse_integer_with_error(signed, input));

    let ns = if embedded {
        quote!(::dashu::integer)
    } else {
        quote!(::dashu_int)
    };

    // if the integer fits in a u32, generates const expression
    if big.bit_len() <= 32 && !static_ {
        let u: u32 = big.try_into().unwrap();
        let sign = quote_sign(embedded, sign);

        return if signed {
            quote! { #ns::IBig::from_parts_const(#sign, #u as _) }
        } else {
            quote! { #ns::UBig::from_dword(#u as _) }
        };
    }

    match (signed, static_) {
        (false, false) => quote_ubig(embedded, big),
        (true, false) => quote_ibig(embedded, IBig::from_parts(sign, big)),
        (false, true) => {
            let data_defs = quote_words(&big.to_le_bytes(), embedded);
            quote! {{
                static DATA: &'static [#ns::Word] = #data_defs;
                static VALUE: #ns::UBig = unsafe { #ns::UBig::from_static_words(DATA) };
                &VALUE
            }}
        }
        (true, true) => {
            let data_defs = quote_words(&big.to_le_bytes(), embedded);
            let sign = quote_sign(embedded, sign);
            quote! {{
                static DATA: &'static [#ns::Word] = #data_defs;
                static VALUE: #ns::IBig = unsafe { #ns::IBig::from_static_words(#sign, DATA) };
                &VALUE
            }}
        }
    }
}

fn parse_integer_with_error(signed: bool, input: TokenStream) -> Result<(Sign, UBig), ParseError> {
    let mut val: Option<_> = None;
    let mut neg = false;
    let mut base_marked = false;
    let mut base: Option<_> = None;

    // parse tokens
    for token in input {
        match token {
            TokenTree::Literal(lit) => {
                if val.is_none() {
                    val = Some(lit.to_string());
                } else if base.is_none() && base_marked {
                    base = Some(lit.to_string());
                } else {
                    return Err(ParseError::InvalidDigit);
                }
            }
            TokenTree::Ident(ident) => {
                if val.is_none() {
                    val = Some(ident.to_string()) // this accepts numbers starting with non-base 10 digits
                } else if base.is_none() && ident == "base" {
                    base_marked = true
                } else {
                    return Err(ParseError::InvalidDigit);
                }
            }
            TokenTree::Punct(punct) => {
                if val.is_none() && punct.as_char() == '-' {
                    if signed {
                        neg = true;
                    } else {
                        return Err(ParseError::InvalidDigit);
                    }
                } else if val.is_none() && punct.as_char() == '+' {
                    if !signed {
                        return Err(ParseError::InvalidDigit);
                    }
                } else {
                    return Err(ParseError::InvalidDigit);
                }
            }
            _ => return Err(ParseError::InvalidDigit),
        }
    }

    // forward the literal to proper format
    let val = val.unwrap();
    let big = match base {
        Some(b) => {
            let b = b.parse::<u32>().or(Err(ParseError::UnsupportedRadix))?;
            UBig::from_str_radix(&val, b)?
        }
        None => {
            if base_marked {
                return Err(ParseError::UnsupportedRadix);
            } else {
                UBig::from_str_with_radix_prefix(&val)?.0
            }
        }
    };

    Ok((Sign::from(neg), big))
}

/// Generate tokens for creating a [UBig] instance (non-const)
pub fn quote_ubig(embedded: bool, int: UBig) -> TokenStream {
    debug_assert!(int.bit_len() > 32);
    let bytes = int.to_le_bytes();
    let len = bytes.len();
    let bytes_tt = quote_bytes(&bytes);

    let ns = if embedded {
        quote!(::dashu::integer)
    } else {
        quote!(::dashu_int)
    };
    quote! {{
        const BYTES: [u8; #len] = #bytes_tt;
        #ns::UBig::from_le_bytes(&BYTES)
    }}
}

/// Generate tokens for creating a [IBig] instance (non-const)
pub fn quote_ibig(embedded: bool, int: IBig) -> TokenStream {
    debug_assert!(int.bit_len() > 32);
    let (sign, mag) = int.into_parts();
    let sign = quote_sign(embedded, sign);
    let mag_tt = quote_ubig(embedded, mag);

    let ns: TokenStream = if embedded {
        quote!(::dashu::integer)
    } else {
        quote!(::dashu_int)
    };
    quote! { #ns::IBig::from_parts(#sign, #mag_tt) }
}