1 files changed, 47 insertions, 0 deletions
diff --git a/Lib/fontTools/misc/roundTools.py b/Lib/fontTools/misc/roundTools.py
index c1d546f1..6f4aa634 100644
--- a/Lib/fontTools/misc/roundTools.py
+++ b/Lib/fontTools/misc/roundTools.py
@@ -56,3 +56,50 @@ def roundFunc(tolerance, round=otRound):
         return round
 
     return functools.partial(maybeRound, tolerance=tolerance, round=round)
+
+
+def nearestMultipleShortestRepr(value: float, factor: float) -> str:
+    """Round to nearest multiple of factor and return shortest decimal representation.
+
+    This chooses the float that is closer to a multiple of the given factor while
+    having the shortest decimal representation (the least number of fractional decimal
+    digits).
+
+    For example, given the following:
+
+    >>> nearestMultipleShortestRepr(-0.61883544921875, 1.0/(1<<14))
+    '-0.61884'
+
+    Useful when you need to serialize or print a fixed-point number (or multiples
+    thereof, such as F2Dot14 fractions of 180 degrees in COLRv1 PaintRotate) in
+    a human-readable form.
+
+    Args:
+        value (value): The value to be rounded and serialized.
+        factor (float): The value which the result is a close multiple of.
+
+    Returns:
+        str: A compact string representation of the value.
+    """
+    if not value:
+        return "0.0"
+
+    value = otRound(value / factor) * factor
+    eps = .5 * factor
+    lo = value - eps
+    hi = value + eps
+    # If the range of valid choices spans an integer, return the integer.
+    if int(lo) != int(hi):
+        return str(float(round(value)))
+
+    fmt = "%.8f"
+    lo = fmt % lo
+    hi = fmt % hi
+    assert len(lo) == len(hi) and lo != hi
+    for i in range(len(lo)):
+        if lo[i] != hi[i]:
+            break
+    period = lo.find('.')
+    assert period < i
+    fmt = "%%.%df" % (i - period)
+    return fmt % value