Attachment 99199 Details for Bug 78809 – Avoid round-off errors when determining raster dimensions.

Avoid round-off errors when determining raster dimensions.

0001-Avoid-round-off-errors-when-determining-raster-dimen.patch (text/plain), 1.98 KB, created by James Cloos on 2014-05-17 04:43:36 UTC

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Creator: James Cloos

Created: 2014-05-17 04:43:36 UTC

Size: 1.98 KB

patch

obsolete

>From 4e6d85ece537cfb0623dc77e3948bec9b0ed50ce Mon Sep 17 00:00:00 2001
>From: James Cloos <cloos@jhcloos.com>
>Date: Sat, 17 May 2014 00:08:26 -0400
>Subject: [PATCH] Avoid round-off errors when determining raster dimensions.
>
>The code in pdftoppm.cc and pdftocairo.cc carefully avoided overflow
>when converting page sizes from points to pixels.
>
>This worked well when the math was performed at extended precision,
>as is done when using x387 opcodes, but could lead to results too
>large by a ulp when computed without extra precision.
>
>The code then needs to call ceil(3) to round fractional results up
>to the next larger integer, resulting in an off-by-one error if the
>computed size is even one ulp more than an integer.
>
>The initial size is already a multiple of 72, so rearranging the math
>to multiply before dividing by 72 avoids that imprecision.
>
>Signed-off-by: James Cloos <cloos@jhcloos.com>
>---
> utils/pdftocairo.cc | 4 ++--
> utils/pdftoppm.cc   | 4 ++--
> 2 files changed, 4 insertions(+), 4 deletions(-)
>
>diff --git a/utils/pdftocairo.cc b/utils/pdftocairo.cc
>index b3f57b6..5984dbd 100644
>--- a/utils/pdftocairo.cc
>+++ b/utils/pdftocairo.cc
>@@ -428,8 +428,8 @@ static void getOutputSize(double page_w, double page_h, double *width, double *h
>       *height = paperHeight;
>     }
>   } else {
>-    getCropSize(page_w * (x_resolution / 72.0),
>-		page_h * (y_resolution / 72.0),
>+    getCropSize(page_w * x_resolution / 72.0,
>+		page_h * y_resolution / 72.0,
> 		width, height);
>   }
> }
>diff --git a/utils/pdftoppm.cc b/utils/pdftoppm.cc
>index 962860b..5d71155 100644
>--- a/utils/pdftoppm.cc
>+++ b/utils/pdftoppm.cc
>@@ -497,8 +497,8 @@ int main(int argc, char *argv[]) {
>           x_resolution = y_resolution;
>       }
>     }
>-    pg_w = pg_w * (x_resolution / 72.0);
>-    pg_h = pg_h * (y_resolution / 72.0);
>+    pg_w = pg_w * x_resolution / 72.0;
>+    pg_h = pg_h * y_resolution / 72.0;
>     if ((doc->getPageRotate(pg) == 90) || (doc->getPageRotate(pg) == 270)) {
>       tmp = pg_w;
>       pg_w = pg_h;
>-- 
>1.9.3
>

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