From 64f783cc35008302385699f771b95919381dcd29 Mon Sep 17 00:00:00 2001
From: Markus Pfeiffer <markus.pfeiffer@morphism.de>
Date: Fri, 24 Nov 2017 23:44:29 +0000
Subject: [PATCH] Introduce kernel-level LCM_INT

This is done using the gmp function mpz_lcm.
---
 lib/integer.gi |  8 +----
 src/integer.c  | 86 ++++++++++++++++++++++++++++++++++++--------------
 2 files changed, 64 insertions(+), 30 deletions(-)

diff --git a/lib/integer.gi b/lib/integer.gi
index 459ffceaf5d..ec684b88750 100644
--- a/lib/integer.gi
+++ b/lib/integer.gi
@@ -1078,13 +1078,7 @@ InstallGlobalFunction( IsPrimePowerInt,
 ##
 #F  LcmInt( <m>, <n> )  . . . . . . . . . . least common multiple of integers
 ##
-InstallGlobalFunction(LcmInt,function ( n, m )
-    if m = 0  and n = 0  then
-        return 0;
-    else
-        return AbsInt( m / GcdInt( m, n ) * n );
-    fi;
-end);
+InstallGlobalFunction(LcmInt, LCM_INT);
 
 
 #############################################################################
diff --git a/src/integer.c b/src/integer.c
index 9e857ee1eeb..7e1d26b3bb1 100644
--- a/src/integer.c
+++ b/src/integer.c
@@ -2202,6 +2202,45 @@ Obj FuncGCD_INT ( Obj self, Obj opL, Obj opR )
   return GcdInt( opL, opR );
 }
 
+Obj LcmInt(Obj opL, Obj opR)
+{
+    UInt       sizeL, sizeR;
+    fake_mpz_t mpzL, mpzR, mpzResult;
+    Obj        result;
+
+    CHECK_INT(opL);
+    CHECK_INT(opR);
+
+    if (opL == INTOBJ_INT(0))
+        return AbsInt(opR);
+    if (opR == INTOBJ_INT(0))
+        return AbsInt(opL);
+
+    sizeL = SIZE_INT_OR_INTOBJ(opL);
+    sizeR = SIZE_INT_OR_INTOBJ(opR);
+
+    NEW_FAKEMPZ(mpzResult, sizeL + sizeR);
+    FAKEMPZ_GMPorINTOBJ(mpzL, opL);
+    FAKEMPZ_GMPorINTOBJ(mpzR, opR);
+
+    /* compute the gcd */
+    mpz_lcm(MPZ_FAKEMPZ(mpzResult), MPZ_FAKEMPZ(mpzL), MPZ_FAKEMPZ(mpzR));
+
+    /* convert result to GAP object and return it */
+    CHECK_FAKEMPZ(mpzResult);
+    CHECK_FAKEMPZ(mpzL);
+    CHECK_FAKEMPZ(mpzR);
+    result = GMPorINTOBJ_FAKEMPZ(mpzResult);
+    CHECK_INT(result);
+    return result;
+}
+
+Obj FuncLCM_INT(Obj self, Obj opL, Obj opR)
+{
+    REQUIRE_INT_ARG("LcmInt", "left", opL);
+    REQUIRE_INT_ARG("LcmInt", "right", opR);
+    return LcmInt(opL, opR);
+}
 
 /****************************************************************************
 **
@@ -2614,29 +2653,30 @@ static StructGVarFilt GVarFilts [] = {
 **
 *V  GVarFuncs . . . . . . . . . . . . . . . . . . list of functions to export
 */
-static StructGVarFunc GVarFuncs [] = {
-
-  GVAR_FUNC(QUO_INT, 2, "gmp1, gmp2"),
-  GVAR_FUNC(ABS_INT, 1, "x"),
-  GVAR_FUNC(SIGN_INT, 1, "x"),
-  GVAR_FUNC(REM_INT, 2, "gmp1, gmp2"),
-  GVAR_FUNC(GCD_INT, 2, "gmp1, gmp2"),
-  GVAR_FUNC(PROD_INT_OBJ, 2, "gmp, obj"),
-  GVAR_FUNC(POW_OBJ_INT, 2, "obj, gmp"),
-  GVAR_FUNC(JACOBI_INT, 2, "n, m"),
-  GVAR_FUNC(FACTORIAL_INT, 1, "n"),
-  GVAR_FUNC(BINOMIAL_INT, 2, "n, k"),
-  GVAR_FUNC(PVALUATION_INT, 2, "n, p"),
-  GVAR_FUNC(POWERMODINT, 3, "base, exp, mod"),
-  GVAR_FUNC(IS_PROBAB_PRIME_INT, 2, "n, reps"),
-  GVAR_FUNC(INVMODINT, 2, "base, mod"),
-  GVAR_FUNC(HexStringInt, 1, "gmp"),
-  GVAR_FUNC(IntHexString, 1, "string"),
-  GVAR_FUNC(Log2Int, 1, "gmp"),
-  GVAR_FUNC(STRING_INT, 1, "gmp"),
-  GVAR_FUNC(INT_STRING, 1, "string"),
-  GVAR_FUNC(RandomIntegerMT, 2, "mtstr, nrbits"),
-  { 0, 0, 0, 0, 0 }
+static StructGVarFunc GVarFuncs[] = {
+
+    GVAR_FUNC(QUO_INT, 2, "gmp1, gmp2"),
+    GVAR_FUNC(ABS_INT, 1, "x"),
+    GVAR_FUNC(SIGN_INT, 1, "x"),
+    GVAR_FUNC(REM_INT, 2, "gmp1, gmp2"),
+    GVAR_FUNC(GCD_INT, 2, "gmp1, gmp2"),
+    GVAR_FUNC(LCM_INT, 2, "gmp1, gmp2"),
+    GVAR_FUNC(PROD_INT_OBJ, 2, "gmp, obj"),
+    GVAR_FUNC(POW_OBJ_INT, 2, "obj, gmp"),
+    GVAR_FUNC(JACOBI_INT, 2, "n, m"),
+    GVAR_FUNC(FACTORIAL_INT, 1, "n"),
+    GVAR_FUNC(BINOMIAL_INT, 2, "n, k"),
+    GVAR_FUNC(PVALUATION_INT, 2, "n, p"),
+    GVAR_FUNC(POWERMODINT, 3, "base, exp, mod"),
+    GVAR_FUNC(IS_PROBAB_PRIME_INT, 2, "n, reps"),
+    GVAR_FUNC(INVMODINT, 2, "base, mod"),
+    GVAR_FUNC(HexStringInt, 1, "gmp"),
+    GVAR_FUNC(IntHexString, 1, "string"),
+    GVAR_FUNC(Log2Int, 1, "gmp"),
+    GVAR_FUNC(STRING_INT, 1, "gmp"),
+    GVAR_FUNC(INT_STRING, 1, "string"),
+    GVAR_FUNC(RandomIntegerMT, 2, "mtstr, nrbits"),
+    { 0, 0, 0, 0, 0 }
 
 };