Обсуждение: Re: [PATCHES] [BUGS] BUG #2846: inconsistent and confusing handling of underflows,
Roman Kononov <kononov195-pgsql@yahoo.com> writes:
> On 12/27/2006 03:23 PM, Bruce Momjian wrote:
>> Are you sure? As I remember, computation automatically upgrades to
>> 'double'. See this program and output:
> This is platform- and compiler- dependent:
... and probably irrelevant, too. We should store the result into a
float4 variable and then test for isinf() on that; that eliminates the
question of whether the compiler did the multiply in a wider format or
not.
regards, tom lane
On 12/27/2006 05:19 PM, Tom Lane wrote: > Roman Kononov <kononov195-pgsql@yahoo.com> writes: >> On 12/27/2006 03:23 PM, Bruce Momjian wrote: >>> Are you sure? As I remember, computation automatically upgrades to >>> 'double'. See this program and output: > >> This is platform- and compiler- dependent: > > ... and probably irrelevant, too. We should store the result into a > float4 variable and then test for isinf() on that; that eliminates the > question of whether the compiler did the multiply in a wider format or > not. You are right provided that you want to ignore underflows and silently produce zeros instead. If you go this way, I recommend to ignore overflows as well, and silently produce infinities and NaNs. Roman
Tom Lane wrote: > Roman Kononov <kononov195-pgsql@yahoo.com> writes: > > On 12/27/2006 03:23 PM, Bruce Momjian wrote: > >> Are you sure? As I remember, computation automatically upgrades to > >> 'double'. See this program and output: > > > This is platform- and compiler- dependent: > > ... and probably irrelevant, too. We should store the result into a > float4 variable and then test for isinf() on that; that eliminates the > question of whether the compiler did the multiply in a wider format or > not. True for overflow to Infinity, but underflow checking is better for float4 using float8. See previous email for details. -- Bruce Momjian bruce@momjian.us EnterpriseDB http://www.enterprisedb.com + If your life is a hard drive, Christ can be your backup. +
Roman Kononov wrote: > On 12/27/2006 05:19 PM, Tom Lane wrote: > > Roman Kononov <kononov195-pgsql@yahoo.com> writes: > >> On 12/27/2006 03:23 PM, Bruce Momjian wrote: > >>> Are you sure? As I remember, computation automatically upgrades to > >>> 'double'. See this program and output: > > > >> This is platform- and compiler- dependent: > > > > ... and probably irrelevant, too. We should store the result into a > > float4 variable and then test for isinf() on that; that eliminates the > > question of whether the compiler did the multiply in a wider format or > > not. > > You are right provided that you want to ignore underflows and silently > produce zeros instead. > > If you go this way, I recommend to ignore overflows as well, and silently > produce infinities and NaNs. While IEEE seems fine with that, I don't think this is good for SQL. It is best to produce a meaningful error. The major issue is that our current code is buggy because it doesn't have consistent behavior, as Roman outlined. -- Bruce Momjian bruce@momjian.us EnterpriseDB http://www.enterprisedb.com + If your life is a hard drive, Christ can be your backup. +