Fortran: speed up decimal output of integers

libgfortran/ChangeLog:

	PR libfortran/98076
	* runtime/string.c (itoa64, itoa64_pad19): New helper functions.
	(gfc_itoa): On targets with 128-bit integers, call fast
	64-bit functions to avoid many slow divisions.

gcc/testsuite/ChangeLog:

	PR libfortran/98076
	* gfortran.dg/pr98076.f90: New test.

2 files changed, 353 insertions, 5 deletions

diff --git a/gcc/testsuite/gfortran.dg/pr98076.f90 b/gcc/testsuite/gfortran.dg/pr98076.f90
new file mode 100644
index 0000000..d1288a4
--- /dev/null
+++ b/gcc/testsuite/gfortran.dg/pr98076.f90
@@ -0,0 +1,293 @@
+! { dg-do run }
+! { dg-require-effective-target fortran_large_int }
+!
+! Check that we can print large integer values
+
+program test
+  implicit none
+  ! 128-bit integer kind
+  integer, parameter :: k = selected_int_kind(38)
+
+  character(len=39) :: s
+  character(len=100) :: buffer
+  integer(kind=k) :: n
+  integer :: i
+
+  ! Random checks
+  do i = 1, 1000
+    call random_digits(s)
+    read(s,*) n
+    write(buffer,'(I0.38)') n
+    print *, s
+    print *, buffer
+    if (adjustl(buffer) /= adjustl(s)) stop 2
+  end do
+
+  ! Systematic check
+  call check(0_k, "0")
+  call check(1_k, "1")
+  call check(9_k, "9")
+  call check(10_k, "10")
+  call check(11_k, "11")
+  call check(99_k, "99")
+  call check(100_k, "100")
+  call check(101_k, "101")
+  call check(999_k, "999")
+  call check(1000_k, "1000")
+  call check(1001_k, "1001")
+  call check(9999_k, "9999")
+  call check(10000_k, "10000")
+  call check(10001_k, "10001")
+  call check(99999_k, "99999")
+  call check(100000_k, "100000")
+  call check(100001_k, "100001")
+  call check(999999_k, "999999")
+  call check(1000000_k, "1000000")
+  call check(1000001_k, "1000001")
+  call check(9999999_k, "9999999")
+  call check(10000000_k, "10000000")
+  call check(10000001_k, "10000001")
+  call check(99999999_k, "99999999")
+  call check(100000000_k, "100000000")
+  call check(100000001_k, "100000001")
+  call check(999999999_k, "999999999")
+  call check(1000000000_k, "1000000000")
+  call check(1000000001_k, "1000000001")
+  call check(9999999999_k, "9999999999")
+  call check(10000000000_k, "10000000000")
+  call check(10000000001_k, "10000000001")
+  call check(99999999999_k, "99999999999")
+  call check(100000000000_k, "100000000000")
+  call check(100000000001_k, "100000000001")
+  call check(999999999999_k, "999999999999")
+  call check(1000000000000_k, "1000000000000")
+  call check(1000000000001_k, "1000000000001")
+  call check(9999999999999_k, "9999999999999")
+  call check(10000000000000_k, "10000000000000")
+  call check(10000000000001_k, "10000000000001")
+  call check(99999999999999_k, "99999999999999")
+  call check(100000000000000_k, "100000000000000")
+  call check(100000000000001_k, "100000000000001")
+  call check(999999999999999_k, "999999999999999")
+  call check(1000000000000000_k, "1000000000000000")
+  call check(1000000000000001_k, "1000000000000001")
+  call check(9999999999999999_k, "9999999999999999")
+  call check(10000000000000000_k, "10000000000000000")
+  call check(10000000000000001_k, "10000000000000001")
+  call check(99999999999999999_k, "99999999999999999")
+  call check(100000000000000000_k, "100000000000000000")
+  call check(100000000000000001_k, "100000000000000001")
+  call check(999999999999999999_k, "999999999999999999")
+  call check(1000000000000000000_k, "1000000000000000000")
+  call check(1000000000000000001_k, "1000000000000000001")
+  call check(9999999999999999999_k, "9999999999999999999")
+  call check(10000000000000000000_k, "10000000000000000000")
+  call check(10000000000000000001_k, "10000000000000000001")
+  call check(99999999999999999999_k, "99999999999999999999")
+  call check(100000000000000000000_k, "100000000000000000000")
+  call check(100000000000000000001_k, "100000000000000000001")
+  call check(999999999999999999999_k, "999999999999999999999")
+  call check(1000000000000000000000_k, "1000000000000000000000")
+  call check(1000000000000000000001_k, "1000000000000000000001")
+  call check(9999999999999999999999_k, "9999999999999999999999")
+  call check(10000000000000000000000_k, "10000000000000000000000")
+  call check(10000000000000000000001_k, "10000000000000000000001")
+  call check(99999999999999999999999_k, "99999999999999999999999")
+  call check(100000000000000000000000_k, "100000000000000000000000")
+  call check(100000000000000000000001_k, "100000000000000000000001")
+  call check(999999999999999999999999_k, "999999999999999999999999")
+  call check(1000000000000000000000000_k, "1000000000000000000000000")
+  call check(1000000000000000000000001_k, "1000000000000000000000001")
+  call check(9999999999999999999999999_k, "9999999999999999999999999")
+  call check(10000000000000000000000000_k, "10000000000000000000000000")
+  call check(10000000000000000000000001_k, "10000000000000000000000001")
+  call check(99999999999999999999999999_k, "99999999999999999999999999")
+  call check(100000000000000000000000000_k, "100000000000000000000000000")
+  call check(100000000000000000000000001_k, "100000000000000000000000001")
+  call check(999999999999999999999999999_k, "999999999999999999999999999")
+  call check(1000000000000000000000000000_k, "1000000000000000000000000000")
+  call check(1000000000000000000000000001_k, "1000000000000000000000000001")
+  call check(9999999999999999999999999999_k, "9999999999999999999999999999")
+  call check(10000000000000000000000000000_k, "10000000000000000000000000000")
+  call check(10000000000000000000000000001_k, "10000000000000000000000000001")
+  call check(99999999999999999999999999999_k, "99999999999999999999999999999")
+  call check(100000000000000000000000000000_k, "100000000000000000000000000000")
+  call check(100000000000000000000000000001_k, "100000000000000000000000000001")
+  call check(999999999999999999999999999999_k, "999999999999999999999999999999")
+  call check(1000000000000000000000000000000_k, "1000000000000000000000000000000")
+  call check(1000000000000000000000000000001_k, "1000000000000000000000000000001")
+  call check(9999999999999999999999999999999_k, "9999999999999999999999999999999")
+  call check(10000000000000000000000000000000_k, "10000000000000000000000000000000")
+  call check(10000000000000000000000000000001_k, "10000000000000000000000000000001")
+  call check(99999999999999999999999999999999_k, "99999999999999999999999999999999")
+  call check(100000000000000000000000000000000_k, "100000000000000000000000000000000")
+  call check(100000000000000000000000000000001_k, "100000000000000000000000000000001")
+  call check(999999999999999999999999999999999_k, "999999999999999999999999999999999")
+  call check(1000000000000000000000000000000000_k, "1000000000000000000000000000000000")
+  call check(1000000000000000000000000000000001_k, "1000000000000000000000000000000001")
+  call check(9999999999999999999999999999999999_k, "9999999999999999999999999999999999")
+  call check(10000000000000000000000000000000000_k, "10000000000000000000000000000000000")
+  call check(10000000000000000000000000000000001_k, "10000000000000000000000000000000001")
+  call check(99999999999999999999999999999999999_k, "99999999999999999999999999999999999")
+  call check(100000000000000000000000000000000000_k, "100000000000000000000000000000000000")
+  call check(100000000000000000000000000000000001_k, "100000000000000000000000000000000001")
+  call check(999999999999999999999999999999999999_k, "999999999999999999999999999999999999")
+  call check(1000000000000000000000000000000000000_k, "1000000000000000000000000000000000000")
+  call check(1000000000000000000000000000000000001_k, "1000000000000000000000000000000000001")
+  call check(9999999999999999999999999999999999999_k, "9999999999999999999999999999999999999")
+  call check(10000000000000000000000000000000000000_k, "10000000000000000000000000000000000000")
+  call check(10000000000000000000000000000000000001_k, "10000000000000000000000000000000000001")
+  call check(99999999999999999999999999999999999999_k, "99999999999999999999999999999999999999")
+  call check(100000000000000000000000000000000000000_k, "100000000000000000000000000000000000000")
+  call check(100000000000000000000000000000000000001_k, "100000000000000000000000000000000000001")
+  call check(109999999999999999999999999999999999999_k, "109999999999999999999999999999999999999")
+
+  call check(-1_k, "-1")
+  call check(-9_k, "-9")
+  call check(-10_k, "-10")
+  call check(-11_k, "-11")
+  call check(-99_k, "-99")
+  call check(-100_k, "-100")
+  call check(-101_k, "-101")
+  call check(-999_k, "-999")
+  call check(-1000_k, "-1000")
+  call check(-1001_k, "-1001")
+  call check(-9999_k, "-9999")
+  call check(-10000_k, "-10000")
+  call check(-10001_k, "-10001")
+  call check(-99999_k, "-99999")
+  call check(-100000_k, "-100000")
+  call check(-100001_k, "-100001")
+  call check(-999999_k, "-999999")
+  call check(-1000000_k, "-1000000")
+  call check(-1000001_k, "-1000001")
+  call check(-9999999_k, "-9999999")
+  call check(-10000000_k, "-10000000")
+  call check(-10000001_k, "-10000001")
+  call check(-99999999_k, "-99999999")
+  call check(-100000000_k, "-100000000")
+  call check(-100000001_k, "-100000001")
+  call check(-999999999_k, "-999999999")
+  call check(-1000000000_k, "-1000000000")
+  call check(-1000000001_k, "-1000000001")
+  call check(-9999999999_k, "-9999999999")
+  call check(-10000000000_k, "-10000000000")
+  call check(-10000000001_k, "-10000000001")
+  call check(-99999999999_k, "-99999999999")
+  call check(-100000000000_k, "-100000000000")
+  call check(-100000000001_k, "-100000000001")
+  call check(-999999999999_k, "-999999999999")
+  call check(-1000000000000_k, "-1000000000000")
+  call check(-1000000000001_k, "-1000000000001")
+  call check(-9999999999999_k, "-9999999999999")
+  call check(-10000000000000_k, "-10000000000000")
+  call check(-10000000000001_k, "-10000000000001")
+  call check(-99999999999999_k, "-99999999999999")
+  call check(-100000000000000_k, "-100000000000000")
+  call check(-100000000000001_k, "-100000000000001")
+  call check(-999999999999999_k, "-999999999999999")
+  call check(-1000000000000000_k, "-1000000000000000")
+  call check(-1000000000000001_k, "-1000000000000001")
+  call check(-9999999999999999_k, "-9999999999999999")
+  call check(-10000000000000000_k, "-10000000000000000")
+  call check(-10000000000000001_k, "-10000000000000001")
+  call check(-99999999999999999_k, "-99999999999999999")
+  call check(-100000000000000000_k, "-100000000000000000")
+  call check(-100000000000000001_k, "-100000000000000001")
+  call check(-999999999999999999_k, "-999999999999999999")
+  call check(-1000000000000000000_k, "-1000000000000000000")
+  call check(-1000000000000000001_k, "-1000000000000000001")
+  call check(-9999999999999999999_k, "-9999999999999999999")
+  call check(-10000000000000000000_k, "-10000000000000000000")
+  call check(-10000000000000000001_k, "-10000000000000000001")
+  call check(-99999999999999999999_k, "-99999999999999999999")
+  call check(-100000000000000000000_k, "-100000000000000000000")
+  call check(-100000000000000000001_k, "-100000000000000000001")
+  call check(-999999999999999999999_k, "-999999999999999999999")
+  call check(-1000000000000000000000_k, "-1000000000000000000000")
+  call check(-1000000000000000000001_k, "-1000000000000000000001")
+  call check(-9999999999999999999999_k, "-9999999999999999999999")
+  call check(-10000000000000000000000_k, "-10000000000000000000000")
+  call check(-10000000000000000000001_k, "-10000000000000000000001")
+  call check(-99999999999999999999999_k, "-99999999999999999999999")
+  call check(-100000000000000000000000_k, "-100000000000000000000000")
+  call check(-100000000000000000000001_k, "-100000000000000000000001")
+  call check(-999999999999999999999999_k, "-999999999999999999999999")
+  call check(-1000000000000000000000000_k, "-1000000000000000000000000")
+  call check(-1000000000000000000000001_k, "-1000000000000000000000001")
+  call check(-9999999999999999999999999_k, "-9999999999999999999999999")
+  call check(-10000000000000000000000000_k, "-10000000000000000000000000")
+  call check(-10000000000000000000000001_k, "-10000000000000000000000001")
+  call check(-99999999999999999999999999_k, "-99999999999999999999999999")
+  call check(-100000000000000000000000000_k, "-100000000000000000000000000")
+  call check(-100000000000000000000000001_k, "-100000000000000000000000001")
+  call check(-999999999999999999999999999_k, "-999999999999999999999999999")
+  call check(-1000000000000000000000000000_k, "-1000000000000000000000000000")
+  call check(-1000000000000000000000000001_k, "-1000000000000000000000000001")
+  call check(-9999999999999999999999999999_k, "-9999999999999999999999999999")
+  call check(-10000000000000000000000000000_k, "-10000000000000000000000000000")
+  call check(-10000000000000000000000000001_k, "-10000000000000000000000000001")
+  call check(-99999999999999999999999999999_k, "-99999999999999999999999999999")
+  call check(-100000000000000000000000000000_k, "-100000000000000000000000000000")
+  call check(-100000000000000000000000000001_k, "-100000000000000000000000000001")
+  call check(-999999999999999999999999999999_k, "-999999999999999999999999999999")
+  call check(-1000000000000000000000000000000_k, "-1000000000000000000000000000000")
+  call check(-1000000000000000000000000000001_k, "-1000000000000000000000000000001")
+  call check(-9999999999999999999999999999999_k, "-9999999999999999999999999999999")
+  call check(-10000000000000000000000000000000_k, "-10000000000000000000000000000000")
+  call check(-10000000000000000000000000000001_k, "-10000000000000000000000000000001")
+  call check(-99999999999999999999999999999999_k, "-99999999999999999999999999999999")
+  call check(-100000000000000000000000000000000_k, "-100000000000000000000000000000000")
+  call check(-100000000000000000000000000000001_k, "-100000000000000000000000000000001")
+  call check(-999999999999999999999999999999999_k, "-999999999999999999999999999999999")
+  call check(-1000000000000000000000000000000000_k, "-1000000000000000000000000000000000")
+  call check(-1000000000000000000000000000000001_k, "-1000000000000000000000000000000001")
+  call check(-9999999999999999999999999999999999_k, "-9999999999999999999999999999999999")
+  call check(-10000000000000000000000000000000000_k, "-10000000000000000000000000000000000")
+  call check(-10000000000000000000000000000000001_k, "-10000000000000000000000000000000001")
+  call check(-99999999999999999999999999999999999_k, "-99999999999999999999999999999999999")
+  call check(-100000000000000000000000000000000000_k, "-100000000000000000000000000000000000")
+  call check(-100000000000000000000000000000000001_k, "-100000000000000000000000000000000001")
+  call check(-999999999999999999999999999999999999_k, "-999999999999999999999999999999999999")
+  call check(-1000000000000000000000000000000000000_k, "-1000000000000000000000000000000000000")
+  call check(-1000000000000000000000000000000000001_k, "-1000000000000000000000000000000000001")
+  call check(-9999999999999999999999999999999999999_k, "-9999999999999999999999999999999999999")
+  call check(-10000000000000000000000000000000000000_k, "-10000000000000000000000000000000000000")
+  call check(-10000000000000000000000000000000000001_k, "-10000000000000000000000000000000000001")
+  call check(-99999999999999999999999999999999999999_k, "-99999999999999999999999999999999999999")
+  call check(-100000000000000000000000000000000000000_k, "-100000000000000000000000000000000000000")
+  call check(-100000000000000000000000000000000000001_k, "-100000000000000000000000000000000000001")
+  call check(-109999999999999999999999999999999999999_k, "-109999999999999999999999999999999999999")
+
+contains
+
+  subroutine check (i, str)
+    implicit none
+    integer(kind=k), intent(in), value :: i
+    character(len=*), intent(in) :: str
+
+    character(len=100) :: buffer
+    write(buffer,*) i
+    if (adjustl(buffer) /= adjustl(str)) stop 1
+  end subroutine
+
+  subroutine random_digits (str)
+    implicit none
+    integer, parameter :: l = 38
+    character(len=l+1) :: str
+    real :: r
+    integer :: i, d
+
+    str = ""
+    do i = 2, l+1
+      call random_number(r)
+      d = floor(r * 10)
+      str(i:i) = achar(48 + d)
+    end do
+
+    call random_number(r)
+    if (r > 0.5) then
+      str(1:1) = '-'
+    end if
+  end subroutine
+end
diff --git a/libgfortran/runtime/string.c b/libgfortran/runtime/string.c
index 835027a..0ccd731 100644
--- a/libgfortran/runtime/string.c
+++ b/libgfortran/runtime/string.c
@@ -23,6 +23,7 @@ see the files COPYING3 and COPYING.RUNTIME respectively.  If not, see
 <http://www.gnu.org/licenses/>.  */
 
 #include "libgfortran.h"
+#include <assert.h>
 #include <string.h>
 #include <strings.h>
 
@@ -169,6 +170,38 @@ find_option (st_parameter_common *cmp, const char *s1, gfc_charlen_type s1_len,
 }
 
 
+/* Fast helper function for a positive value that fits in uint64_t.  */
+
+static inline char *
+itoa64 (uint64_t n, char *p)
+{
+  while (n != 0)
+    {
+      *--p = '0' + (n % 10);
+      n /= 10;
+    }
+  return p;
+}
+
+
+#if defined(HAVE_GFC_INTEGER_16)
+# define TEN19 ((GFC_UINTEGER_LARGEST) 1000000 * (GFC_UINTEGER_LARGEST) 1000000 * (GFC_UINTEGER_LARGEST) 10000000)
+
+/* Same as itoa64(), with zero padding of 19 digits.  */
+
+static inline char *
+itoa64_pad19 (uint64_t n, char *p)
+{
+  for (int k = 0; k < 19; k++)
+    {
+      *--p = '0' + (n % 10);
+      n /= 10;
+    }
+  return p;
+}
+#endif
+
+
 /* Integer to decimal conversion.
 
    This function is much more restricted than the widespread (but
@@ -195,11 +228,33 @@ gfc_itoa (GFC_UINTEGER_LARGEST n, char *buffer, size_t len)
   p = buffer + GFC_ITOA_BUF_SIZE - 1;
   *p = '\0';
 
-  while (n != 0)
+#if defined(HAVE_GFC_INTEGER_16)
+  /* On targets that have a 128-bit integer type, division in that type
+     is slow, because it occurs through a function call. We avoid that.  */
+
+  if (n <= UINT64_MAX)
+    /* If the value fits in uint64_t, use the fast function. */
+    return itoa64 (n, p);
+  else
     {
-      *--p = '0' + (n % 10);
-      n /= 10;
+      /* Otherwise, break down into smaller bits by division. Two calls to
+	 the uint64_t function are not sufficient for all 128-bit unsigned
+	 integers (we would need three calls), but they do suffice for all
+	 values up to 2^127, which is the largest that Fortran can produce
+	 (-HUGE(0_16)-1) with its signed integer types.  */
+      static_assert(sizeof(GFC_UINTEGER_LARGEST) <= 2 * sizeof(uint64_t));
+
+      GFC_UINTEGER_LARGEST r;
+      r = n % TEN19;
+      n = n / TEN19;
+      assert (r <= UINT64_MAX);
+      p = itoa64_pad19 (r, p);
+
+      assert(n <= UINT64_MAX);
+      return itoa64 (n, p);
     }
-
-  return p;
+#else
+  /* On targets where the largest integer is 64-bit, just use that.  */
+  return itoa64 (n, p);
+#endif
 }