papermario/tools/splat/util/floats.py

import math
import struct

# From mips_to_c: https://github.com/matt-kempster/mips_to_c/blob/d208400cca045113dada3e16c0d59c50cdac4529/src/translate.py#L2085
def format_f32_imm(num: int) -> str:
    packed = struct.pack(">I", num & (2**32 - 1))
    value = struct.unpack(">f", packed)[0]

    if not value or value == 4294967296.0:
        # Zero, negative zero, nan, or INT_MAX.
        return str(value)

    # Write values smaller than 1e-7 / greater than 1e7 using scientific notation,
    # and values in between using fixed point.
    if abs(math.log10(abs(value))) > 6.9:
        fmt_char = "e"
    elif abs(value) < 1:
        fmt_char = "f"
    else:
        fmt_char = "g"

    def fmt(prec: int) -> str:
        """Format 'value' with 'prec' significant digits/decimals, in either scientific
        or regular notation depending on 'fmt_char'."""
        ret = ("{:." + str(prec) + fmt_char + "}").format(value)
        if fmt_char == "e":
            return ret.replace("e+", "e").replace("e0", "e").replace("e-0", "e-")
        if "e" in ret:
            # The "g" format character can sometimes introduce scientific notation if
            # formatting with too few decimals. If this happens, return an incorrect
            # value to prevent the result from being used.
            #
            # Since the value we are formatting is within (1e-7, 1e7) in absolute
            # value, it will at least be possible to format with 7 decimals, which is
            # less than float precision. Thus, this annoying Python limitation won't
            # lead to us outputting numbers with more precision than we really have.
            return "0"
        return ret

    # 20 decimals is more than enough for a float. Start there, then try to shrink it.
    prec = 20
    while prec > 0:
        prec -= 1
        value2 = float(fmt(prec))
        if struct.pack(">f", value2) != packed:
            prec += 1
            break

    if prec == 20:
        # Uh oh, even the original value didn't format correctly. Fall back to str(),
        # which ought to work.
        return str(value)

    ret = fmt(prec)
    if "." not in ret and "e" not in ret:
        ret += ".0"
    return ret


def format_f64_imm(num: int) -> str:
    (value,) = struct.unpack(">d", struct.pack(">Q", num & (2**64 - 1)))
    return str(value)