Support rounding modes in mpf.__format__ (#823)

Adds support for rounding modes 'U', 'D', 'Z' and 'N', following the gmpy2 library.
2024-08-01 23:19:24 -03:00
parent 0a79b5626c
commit aa6690b5fa
2 changed files with 130 additions and 12 deletions
@@ -1103,28 +1103,39 @@ def to_digits_exp(s, dps, base=10):
    exponent += len(digits) - fixdps - 1
    return sign, digits, exponent

-def round_digits(digits, dps, base):
+def round_digits(digits, dps, base, rounding=round_nearest):
    '''
    Returns the rounded digits, and the number of places the decimal point was
    shifted.
+
+    Supports three kinds of rounding: up, down, or nearest.
    '''

    assert len(digits) > dps
+    assert rounding in (round_nearest, round_up, round_down)
+
    exponent = 0

-    rnd_digs = stddigits[(base//2 + base % 2):base]
+    if rounding == round_down:
+        return digits[:dps], 0
+    elif rounding == round_nearest:
+        rnd_digs = stddigits[(base//2 + base % 2):base]
+    else:
+        rnd_digs = stddigits[:base]
+
+    tie_up = False

-    round_up = False
    # The first digit after dps is a 5.
    if digits[dps] == rnd_digs[0]:
        for i in range(dps+1, len(digits)):
            if digits[i] != '0':
-                round_up = True
+                tie_up = True
                break
        if digits[dps-1] in stddigits[1:base:2]:
-            round_up = True
+            tie_up = True
+
+    if not tie_up:

-    if not round_up:
        digits = digits[:dps] + stddigits[int(digits[dps], base) - 1]

    # Rounding up kills some instances of "...99999"
@@ -1375,9 +1386,16 @@ _FLOAT_FORMAT_SPECIFICATION_MATCHER = re.compile(r"""
    (?P<width>0|[1-9][0-9]*)?
    (?P<thousands_separators>[,_])?
    (?:\.(?P<precision>0|[1-9][0-9]*))?
+    (?P<rounding>[UDZN])?
    (?P<type>[eEfFgG])
 """, re.DOTALL | re.VERBOSE).fullmatch

+_GMPY_ROUND_CHAR_DICT = {
+        'U': round_ceiling,
+        'D': round_floor,
+        'Z': round_down,
+        'N': round_nearest
+        }

 def calc_padding(nchars, width, align):
    '''
@@ -1415,6 +1433,7 @@ def read_format_spec(format_spec):
        'thousands_separators': '',
        'width': -1,
        'precision': 6,
+        'rounding': round_nearest,
        'type': 'f'
        }

@@ -1429,8 +1448,12 @@ def read_format_spec(format_spec):
            or format_dict['thousands_separators']
        format_dict['width'] = int(match['width'] or format_dict['width'])
        format_dict['precision'] = int(match['precision'] or format_dict['precision'])
+        rounding_char = match['rounding']
        format_dict['type'] = match['type'] or format_dict['type']

+        if rounding_char is not None:
+            format_dict['rounding'] = _GMPY_ROUND_CHAR_DICT[rounding_char]
+
        if match['zeropad'] and match['fill_char']:
            raise ValueError('Cannot specify both 0-padding and a fill '
                             'character')
@@ -1453,7 +1476,8 @@ def format_fixed(s,
                 sep_range=3,
                 base=10,
                 alternate=False,
-                 no_neg_0=False):
+                 no_neg_0=False,
+                 rounding=round_nearest):
    '''
    Format a number into fixed point.
    Returns the sign character, and the string that represents the number in
@@ -1490,7 +1514,7 @@ def format_fixed(s,
        if no_neg_0:
            sign = '' if sign_spec == '-' else sign_spec
    else:
-        digits, exp_add = round_digits(digits, dps, base)
+        digits, exp_add = round_digits(digits, dps, base, rounding)
        exponent += exp_add

        # Here we prepend the corresponding 0s to the digits string, according
@@ -1543,7 +1567,8 @@ def format_scientific(s,
                      base=10,
                      capitalize=False,
                      alternate=False,
-                      no_neg_0=False):
+                      rounding=round_nearest):
+

    sep = 'E' if capitalize else 'e'

@@ -1555,7 +1580,7 @@ def format_scientific(s,
    if sign != '-' and sign_spec != '-':
        sign = sign_spec

-    digits, exp_add = round_digits(digits, dps, base)
+    digits, exp_add = round_digits(digits, dps, base, rounding)
    exponent += exp_add

    if strip_zeros:
@@ -1593,6 +1618,13 @@ def format_mpf(num, format_spec):
    strip_last_zero = False
    strip_zeros = False

+    if format_dict['rounding'] == round_ceiling:
+        rounding = round_down if num[0] else round_up
+    elif format_dict['rounding'] == round_floor:
+        rounding = round_up if num[0] else round_down
+    else:
+        rounding = format_dict['rounding']
+
    if fmt_type == 'g':
        if not format_dict['alternate']:
            strip_last_zero = True
@@ -1620,7 +1652,8 @@ def format_mpf(num, format_spec):
                sep_range=3,
                base=10,
                alternate=format_dict['alternate'],
-                no_neg_0=format_dict['no_neg_0']
+                no_neg_0=format_dict['no_neg_0'],
+                rounding=rounding
                )
    else:  # The format type is scientific
        sign, digits = format_scientific(
@@ -1631,7 +1664,7 @@ def format_mpf(num, format_spec):
                base=10,
                capitalize=capitalize,
                alternate=format_dict['alternate'],
-                no_neg_0=format_dict['no_neg_0']
+                rounding=rounding
                )

    nchars = len(digits) + len(sign)
@@ -559,6 +559,91 @@ def test_mpf_fmt():
        assert f"{mp.mpf('0.24'):=+020.2e}" == '+000000000002.40e-01'
        assert f"{mp.mpf('0.24'):=+020.2g}" == '+0000000000000000.24'

+        # Tests for different kinds of rounding
+        num = mp.mpf('-1.23456789999901234567')
+        assert f"{num:=.2Uf}" == "-1.23"
+        assert f"{num:=.2Df}" == "-1.24"
+        assert f"{num:=.2Zf}" == "-1.23"
+        assert f"{num:=.2Nf}" == "-1.23"
+
+        assert f"{num:=.3Uf}" == "-1.234"
+        assert f"{num:=.3Df}" == "-1.235"
+        assert f"{num:=.3Zf}" == "-1.234"
+        assert f"{num:=.3Nf}" == "-1.235"
+
+        assert f"{num:=.10Uf}" == "-1.2345678999"
+        assert f"{num:=.10Df}" == "-1.2345679000"
+        assert f"{num:=.10Zf}" == "-1.2345678999"
+        assert f"{num:=.10Nf}" == "-1.2345679000"
+
+        num = mp.mpf('1.23456789999901234567')
+        assert f"{num:=.2Uf}" == "1.24"
+        assert f"{num:=.2Df}" == "1.23"
+        assert f"{num:=.2Zf}" == "1.23"
+        assert f"{num:=.2Nf}" == "1.23"
+
+        assert f"{num:=.3Uf}" == "1.235"
+        assert f"{num:=.3Df}" == "1.234"
+        assert f"{num:=.3Zf}" == "1.234"
+        assert f"{num:=.3Nf}" == "1.235"
+
+        assert f"{num:=.10Uf}" == "1.2345679000"
+        assert f"{num:=.10Df}" == "1.2345678999"
+        assert f"{num:=.10Zf}" == "1.2345678999"
+        assert f"{num:=.10Nf}" == "1.2345679000"
+
+        num = mp.mpf('-123.456789999901234567')
+        assert f"{num:=.2Ue}" == "-1.23e+02"
+        assert f"{num:=.2De}" == "-1.24e+02"
+        assert f"{num:=.2Ze}" == "-1.23e+02"
+        assert f"{num:=.2Ne}" == "-1.23e+02"
+
+        assert f"{num:=.3Ue}" == "-1.234e+02"
+        assert f"{num:=.3De}" == "-1.235e+02"
+        assert f"{num:=.3Ze}" == "-1.234e+02"
+        assert f"{num:=.3Ne}" == "-1.235e+02"
+
+        assert f"{num:=.10Ue}" == "-1.2345678999e+02"
+        assert f"{num:=.10De}" == "-1.2345679000e+02"
+        assert f"{num:=.10Ze}" == "-1.2345678999e+02"
+        assert f"{num:=.10Ne}" == "-1.2345679000e+02"
+
+        num = mp.mpf('123456.789999901234567')
+        assert f"{num:=.2Ue}" == "1.24e+05"
+        assert f"{num:=.2De}" == "1.23e+05"
+        assert f"{num:=.2Ze}" == "1.23e+05"
+        assert f"{num:=.2Ne}" == "1.23e+05"
+
+        assert f"{num:=.3Ue}" == "1.235e+05"
+        assert f"{num:=.3De}" == "1.234e+05"
+        assert f"{num:=.3Ze}" == "1.234e+05"
+        assert f"{num:=.3Ne}" == "1.235e+05"
+
+        assert f"{num:=.10Ue}" == "1.2345679000e+05"
+        assert f"{num:=.10De}" == "1.2345678999e+05"
+        assert f"{num:=.10Ze}" == "1.2345678999e+05"
+        assert f"{num:=.10Ne}" == "1.2345679000e+05"
+
+        assert f"{mp.mpf('123.456'):.2Ug}" == "1.3e+02"
+        assert f"{mp.mpf('123.456'):.2Dg}" == "1.2e+02"
+        assert f"{mp.mpf('123.456'):.2Zg}" == "1.2e+02"
+        assert f"{mp.mpf('123.456'):.2Ng}" == "1.2e+02"
+
+        assert f"{mp.mpf('-123.456'):.2Ug}" == "-1.2e+02"
+        assert f"{mp.mpf('-123.456'):.2Dg}" == "-1.3e+02"
+        assert f"{mp.mpf('-123.456'):.2Zg}" == "-1.2e+02"
+        assert f"{mp.mpf('-123.456'):.2Ng}" == "-1.2e+02"
+
+        assert f"{mp.mpf('123.456'):.5Ug}" == "123.46"
+        assert f"{mp.mpf('123.456'):.5Dg}" == "123.45"
+        assert f"{mp.mpf('123.456'):.5Zg}" == "123.45"
+        assert f"{mp.mpf('123.456'):.5Ng}" == "123.46"
+
+        assert f"{mp.mpf('-123.456'):.5Ug}" == "-123.45"
+        assert f"{mp.mpf('-123.456'):.5Dg}" == "-123.46"
+        assert f"{mp.mpf('-123.456'):.5Zg}" == "-123.45"
+        assert f"{mp.mpf('-123.456'):.5Ng}" == "-123.46"
+

 def test_errors():
    with pytest.raises(ValueError):