diff options
| author | Chris Sherlock <chris.sherlock79@gmail.com> | 2018-05-04 03:40:11 +1000 |
|---|---|---|
| committer | Noel Grandin <noel.grandin@collabora.co.uk> | 2018-05-08 20:35:18 +0200 |
| commit | 6064e4f3b03411b8898804ba4dac389686791c67 (patch) | |
| tree | bb517c6fc25698a65125f298089a90334c83f382 /include/tools | |
| parent | 6b2fa7792a8e4feafb6920f0b289bf2c525d14e5 (diff) | |
tools: document and test sanitiseMm100ToTwip()
Change-Id: I2f6349c679a714e5168ae3c5eccd054c5522bbc9
Reviewed-on: https://gerrit.libreoffice.org/53814
Tested-by: Jenkins <ci@libreoffice.org>
Reviewed-by: Noel Grandin <noel.grandin@collabora.co.uk>
Diffstat (limited to 'include/tools')
| -rw-r--r-- | include/tools/helpers.hxx | 16 |
1 files changed, 14 insertions, 2 deletions
diff --git a/include/tools/helpers.hxx b/include/tools/helpers.hxx index 8325f095bad8..0a349ea62d1d 100644 --- a/include/tools/helpers.hxx +++ b/include/tools/helpers.hxx @@ -55,7 +55,19 @@ inline long FRound( double fVal ) return fVal > 0.0 ? static_cast<long>( fVal + 0.5 ) : -static_cast<long>( -fVal + 0.5 ); } -// return (n >= 0)? (n*72+63)/127: (n*72-63)/127; +/** Convert 100th-mm to twips + + A twip is 1/20 of a point, one inch is equal to 72 points, and + one inch is 2,540 100th-mm. + + Thus: + twips = n * 72 / 2,540 / 20 + = n * 72 / 127 + + Adding 63 (half of 127) fixes truncation issues in int arithmetic. + + This formula is (n>=0) ? (n*72+63) / 127 : (n*72-63) / 127 + */ inline sal_Int64 sanitiseMm100ToTwip(sal_Int64 n) { if (n >= 0) @@ -68,7 +80,7 @@ inline sal_Int64 sanitiseMm100ToTwip(sal_Int64 n) if (o3tl::checked_multiply<sal_Int64>(n, 72, n) || o3tl::checked_sub<sal_Int64>(n, 63, n)) n = SAL_MIN_INT64; } - return n / 127; + return n / 127; // 127 is 2,540 100th-mm divided by 20pts } #endif |