tree 70bf39d88a68ae09a38c822d7f9fd7edc1120f3c
parent dd492a22e40e40bc8e07437506d986f877029ff1
author Nigel Tao <nigeltao@golang.org> 1542320878 +1100
committer Nigel Tao <nigeltao@golang.org> 1542336481 +0000

font/sfnt: make PostTable.ItalicAngle a float64

Previously, it was a float32, which obviously has 32 bits of state. Not
all of that 32 bit state space is meaningful, since NaN has multiple bit
representations. The underlying file format field (of type "Fixed" or
16.16 fixed point) is also 32 bits of state
(https://docs.microsoft.com/en-us/typography/opentype/spec/post).
Therefore, converting from 32 bit fixed point to 32 bit floating point
can be lossy. Instead, use 64 bit floating point. 53 significand bits
can losslessly represent all possible 16.16 fixed point values.

Using float64 is also arguably more Go-like, as the default type for the
ideal constant 0.5 is float64, not float32.

Change-Id: I5abe7979a020af2ac4784d6c2723ab8e39e38e34
Reviewed-on: https://go-review.googlesource.com/c/149837
Reviewed-by: Denys Smirnov <denis.smirnov.91@gmail.com>
Reviewed-by: Nigel Tao <nigeltao@golang.org>