[Tarantool-patches] [PATCH v2 2/2] Add IsInt method for checking the fractional part of a number

[Chris Sosnin <k.sosnin@tarantool.org>]

Currently there is no efficient way to do this.

Needed for tarantool/tarantool#4415
---
 decNumber.c | 27 +++++++++++++++++++++++++++
 decNumber.h |  1 +
 2 files changed, 28 insertions(+)

diff --git a/decNumber.c b/decNumber.c
index e248656..26acec3 100644
--- a/decNumber.c
+++ b/decNumber.c
@@ -501,6 +501,33 @@ uLong decNumberToUInt64(const decNumber *dn, decContext *set) {
   return 0;
   }  // decNumberToUInt64
 
+Flag decNumberIsInt(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;                          // work
+      // slice off fraction digits and check for non-zero
+      #if DECDPUN<=4
+        rem=*up-QUOT10(*up, count)*powers[count];
+      #else
+        rem=*up%powers[count];          // slice off discards
+      #endif
+      if (rem!=0) return 0;
+      }
+    }
+    return 1;
+  }  // decNumberIsInt
+
 /* ------------------------------------------------------------------ */
 /* to-scientific-string -- conversion to numeric string               */
 /* to-engineering-string -- conversion to numeric string              */
diff --git a/decNumber.h b/decNumber.h
index ffaa3d8..9d3a7e1 100644
--- a/decNumber.h
+++ b/decNumber.h
@@ -169,6 +169,7 @@
   decNumber  * decNumberTrim(decNumber *);
   const char * decNumberVersion(void);
   decNumber  * decNumberZero(decNumber *);
+  uint8_t      decNumberIsInt(const decNumber *dn);
 
   /* Functions for testing decNumbers (normality depends on context)  */
   int32_t decNumberIsNormal(const decNumber *, decContext *);
-- 
2.21.1 (Apple Git-122.3)