From 040613db3315aeb992208d30789807285316f3b9 Mon Sep 17 00:00:00 2001 From: Explorer09 Date: Thu, 21 Jan 2016 14:06:11 +0800 Subject: [PATCH] Change variable 'dot' to avoid division by reciprocal. (Cherry-picked from d56bcd8e0d8d6a177fc2e40db32fc73ea4588684, the experimental graph coloring branch) The variable 'dot' in GraphMeterMode_draw now means "maximum number of dots per value (column) in graph". The old meaning was "amount of value that is to be represented by a dot" and was always a fraction. Due to a limitation in floating point computing, if GRAPH_HEIGHT were not a power of 2, then rounding errors will occur on numbers like (1.0/3). (Currently GRAPH_HEIGHT is 4 and so no precision loss.) 'dot' was used as a divisor, and it's "division by a reciprocal". We change that to simple multiplication. --- Meter.c | 6 +++--- 1 file changed, 3 insertions(+), 3 deletions(-) diff --git a/Meter.c b/Meter.c index 444d8f60..781d45c7 100644 --- a/Meter.c +++ b/Meter.c @@ -408,9 +408,9 @@ static void GraphMeterMode_draw(Meter* this, int x, int y, int w) { } for (int i = nValues - (w*2) + 2, k = 0; i < nValues; i+=2, k++) { - const double dot = (1.0 / (GraphMeterMode_pixPerRow * GRAPH_HEIGHT)); - int v1 = CLAMP(data->values[i] / dot, 1, GraphMeterMode_pixPerRow * GRAPH_HEIGHT); - int v2 = CLAMP(data->values[i+1] / dot, 1, GraphMeterMode_pixPerRow * GRAPH_HEIGHT); + int pix = GraphMeterMode_pixPerRow * GRAPH_HEIGHT; + int v1 = CLAMP(data->values[i] * pix, 1, pix); + int v2 = CLAMP(data->values[i+1] * pix, 1, pix); int colorIdx = GRAPH_1; for (int line = 0; line < GRAPH_HEIGHT; line++) {