From: Dima Volodin <dvv@dvv.ru>
To: Sam Lantinga <slouken@devolution.com>
Cc: egcs@egcs.cygnus.com
Subject: Re: Rounding errors using doubles?
Date: Thu, 18 Mar 1999 15:54:00 -0000 [thread overview]
Message-ID: <36F1920C.36E310B8@dvv.ru> (raw)
In-Reply-To: <E10NmPs-0005mx-00@roboto.devolution.com>
Sam Lantinga wrote:
> On a Pentium II, the following code gives an incorrect result when using
> doubles, but a correct result when using floats:
>
> #include <stdio.h>
>
> #ifdef USE_FLOAT
> /* This works */
> typedef float percentage_type;
> #else
> /* This doesn't */
> typedef double percentage_type;
> #endif
>
> main()
> {
> int value = 86;
> percentage_type percentage;
>
> printf("Starting Percentage is: %d\n", value);
> percentage = ((percentage_type)value)/100.0;
> printf("Ending Percentage is: %d\n", (int)(percentage * 100.0));
Your code is broken here. What you need is
printf("Ending Percentage is: %d\n", (int) floor(percentage * 100.0 + 0.5));
And, BTW, converting to int is _not_ rounding.
> -Sam Lantinga
Dima
WARNING: multiple messages have this Message-ID
From: Dima Volodin <dvv@dvv.ru>
To: Sam Lantinga <slouken@devolution.com>
Cc: egcs@egcs.cygnus.com
Subject: Re: Rounding errors using doubles?
Date: Wed, 31 Mar 1999 23:46:00 -0000 [thread overview]
Message-ID: <36F1920C.36E310B8@dvv.ru> (raw)
Message-ID: <19990331234600.Not47hyZbcBiHXlL_Bq2odzcoYvW9m1r80yBUcuKVxo@z> (raw)
In-Reply-To: <E10NmPs-0005mx-00@roboto.devolution.com>
Sam Lantinga wrote:
> On a Pentium II, the following code gives an incorrect result when using
> doubles, but a correct result when using floats:
>
> #include <stdio.h>
>
> #ifdef USE_FLOAT
> /* This works */
> typedef float percentage_type;
> #else
> /* This doesn't */
> typedef double percentage_type;
> #endif
>
> main()
> {
> int value = 86;
> percentage_type percentage;
>
> printf("Starting Percentage is: %d\n", value);
> percentage = ((percentage_type)value)/100.0;
> printf("Ending Percentage is: %d\n", (int)(percentage * 100.0));
Your code is broken here. What you need is
printf("Ending Percentage is: %d\n", (int) floor(percentage * 100.0 + 0.5));
And, BTW, converting to int is _not_ rounding.
> -Sam Lantinga
Dima
next prev parent reply other threads:[~1999-03-18 15:54 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
1999-03-18 15:41 Sam Lantinga
[not found] ` < E10NmPs-0005mx-00@roboto.devolution.com >
1999-03-18 15:51 ` Sylvain Pion
1999-03-31 23:46 ` Sylvain Pion
1999-03-18 16:12 ` Joe Buck
[not found] ` < 199903190011.QAA11085@atrus.synopsys.com >
1999-03-18 16:25 ` Joe Buck
1999-03-31 23:46 ` Joe Buck
1999-03-31 23:46 ` Joe Buck
1999-03-18 15:54 ` Dima Volodin [this message]
1999-03-31 23:46 ` Dima Volodin
1999-03-31 23:46 ` Sam Lantinga
1999-03-18 16:45 Sam Lantinga
1999-03-18 16:54 ` Dima Volodin
1999-03-31 23:46 ` Dima Volodin
[not found] ` < E10NnPU-0006Cc-00@roboto.devolution.com >
1999-03-18 16:57 ` David Edelsohn
1999-03-31 23:46 ` David Edelsohn
1999-03-31 23:46 ` Sam Lantinga
1999-03-18 17:43 Ross Smith
[not found] ` < 002d01be71aa$30d420e0$a8a11dcb@animal.ihug.co.nz >
1999-03-19 6:36 ` craig
[not found] ` < 19990319142042.16973.qmail@deer >
1999-03-19 6:36 ` craig
1999-03-31 23:46 ` craig
1999-03-31 23:46 ` craig
1999-03-31 23:46 ` Ross Smith
1999-03-19 9:08 Sam Lantinga
[not found] ` < E10O2lP-0006t2-00@roboto.devolution.com >
1999-03-19 9:43 ` craig
1999-03-31 23:46 ` craig
1999-03-31 23:46 ` Sam Lantinga
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