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 Sat,  6 Jun 2020 17:17:58 +0300 (MSK)
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 <473ff051ab9075f28732c28396d4465460e4a130.1591371404.git.k.sosnin@tarantool.org>
From: Serge Petrenko <sergepetrenko@tarantool.org>
Message-ID: <6719bef9-feee-9f33-b569-acd5d1ca154f@tarantool.org>
Date: Sat, 6 Jun 2020 17:17:57 +0300
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Subject: Re: [Tarantool-patches] [PATCH 2/2] Add IsWhole method for checking
 the fractional part of a number
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To: Chris Sosnin <k.sosnin@tarantool.org>
Cc: tarantool-patches@dev.tarantool.org, v.shpilevoy@tarantool.org

05.06.2020 18:41, Chris Sosnin пишет:
> Currently there is no efficient way to do this.
>
> Needed for tarantool/tarantool#4415
Thanks for the patch!
> ---
>   decNumber.c | 30 ++++++++++++++++++++++++++++++
>   decNumber.h |  1 +
>   2 files changed, 31 insertions(+)
>
> diff --git a/decNumber.c b/decNumber.c
> index 7c53bc3..f4ad927 100644
> --- a/decNumber.c
> +++ b/decNumber.c
> @@ -501,6 +501,36 @@ uLong decNumberToUInt64(const decNumber *dn, decContext *set) {
>     return 0;
>     }  // decNumberToUInt64
>   
> +Flag decNumberIsWhole(const decNumber *dn) {
> +  const Unit *up=dn->lsu;
> +  if (dn->exponent>=0) {
> +    return 1;
> +    }
> +   else {
> +    Int count=-dn->exponent;
> +    // spin up whole units until reach the Unit with the unit digit
> +    for (; count>=DECDPUN; up++) {
> +      if (*up!=0) return 0;
> +      count-=DECDPUN;
> +      }
> +    if (count==0) return 1;             // [a multiple of DECDPUN]
> +     else {                             // [not multiple of DECDPUN]
> +      Int rem, theInt=0;                          // work
> +      // slice off fraction digits and check for non-zero
> +      #if DECDPUN<=4
> +        theInt=QUOT10(*up, count);
> +        rem=*up-theInt*powers[count];
> +      #else
> +        rem=*up%powers[count];          // slice off discards
> +        theInt=*up/powers[count];
> +      #endif
> +      if (rem!=0) return 0;
> +      up++;
> +      }
> +    }
> +    return 1;
> +  }  // decNumberIsWhole
> +

Consider this  diff:

diff --git a/decNumber.c b/decNumber.c
index f4ad927..acc3fb1 100644
--- a/decNumber.c
+++ b/decNumber.c
@@ -515,17 +515,14 @@ Flag decNumberIsWhole(const decNumber *dn) {
        }
      if (count==0) return 1;             // [a multiple of DECDPUN]
       else {                             // [not multiple of DECDPUN]
-      Int rem, theInt=0;                          // work
+      Int rem;                          // work
        // slice off fraction digits and check for non-zero
        #if DECDPUN<=4
-        theInt=QUOT10(*up, count);
-        rem=*up-theInt*powers[count];
+        rem=*up-QUOT10(*up, count)*powers[count];
        #else
          rem=*up%powers[count];          // slice off discards
-        theInt=*up/powers[count];
        #endif
        if (rem!=0) return 0;
-      up++;
        }
      }
      return 1;

>   /* ------------------------------------------------------------------ */
>   /* to-scientific-string -- conversion to numeric string               */
>   /* to-engineering-string -- conversion to numeric string              */
> diff --git a/decNumber.h b/decNumber.h
> index 85a3f3f..71ab27f 100644
> --- a/decNumber.h
> +++ b/decNumber.h
> @@ -169,6 +169,7 @@
>     decNumber  * decNumberTrim(decNumber *);
>     const char * decNumberVersion(void);
>     decNumber  * decNumberZero(decNumber *);
> +  uint8_t      decNumberIsWhole(const decNumber *dn);
>   
>     /* Functions for testing decNumbers (normality depends on context)  */
>     int32_t decNumberIsNormal(const decNumber *, decContext *);

-- 
Serge Petrenko