From d598ef7a6cb37735f23dbcb95281d88eefdfab55 Mon Sep 17 00:00:00 2001
From: Paul Eggert <eggert@cs.ucla.edu>
Date: Thu, 26 Sep 2024 20:01:58 -0700
Subject: [PATCH] factor: improve gmp-related buffering

Previously, the code used stdio buffers for gmp numbers,
and did its own buffering for smaller numbers.  This meant
for more flushing than was needed.  The code now uses its
own buffering for all standard output, which makes for
less flushing and fewer writes.
* src/factor.c (lbuf_half_flush): New function, taken from the
body of lbuf_putnl.
(lbuf_putnl): Use it.
(lbuf_putmpz): New function, to output an mpz without using stdio.
(print_factors): Output via functions instead of via stdio.
---
 src/factor.c | 82 +++++++++++++++++++++++++++++++++++-----------------
 1 file changed, 56 insertions(+), 26 deletions(-)

diff --git a/src/factor.c b/src/factor.c
index f947022e1d..e463186ded 100644
--- a/src/factor.c
+++ b/src/factor.c
@@ -2343,6 +2343,25 @@ lbuf_flush (void)
     write_error ();
 }
 
+/* Write LBUF to standard output.
+   LBUF should contain at least FACTOR_PIPE_BUF bytes.
+   If possible, write a prefix of LBUF that is newline terminated
+   and contains <= FACTOR_PIPE_BUF bytes, so consumers can read atomically.
+   But if the first FACTOR_PIPE_BUF bytes contain no newlines,
+   give up on atomicity and just write the first FACTOR_PIPE_BUF bytes.  */
+static void
+lbuf_half_flush (void)
+{
+  char *nl = memrchr (lbuf_buf, '\n', FACTOR_PIPE_BUF);
+  char *suffix = nl ? nl + 1 : lbuf_buf + FACTOR_PIPE_BUF;
+  idx_t prefix_size = suffix - lbuf_buf;
+  idx_t suffix_size = lbuffered - prefix_size;
+  lbuffered = prefix_size;
+  lbuf_flush ();
+  lbuffered = suffix_size;
+  memmove (lbuf_buf, suffix, suffix_size);
+}
+
 /* Add a character C to lbuf_buf.  */
 static void
 lbuf_putc (char c)
@@ -2365,24 +2384,7 @@ lbuf_putnl (void)
   if (line_buffered)
     lbuf_flush ();
   else if (FACTOR_PIPE_BUF <= lbuffered)
-    {
-      /* Write output in <= PIPE_BUF chunks
-         so consumers can read atomically.  */
-
-      /* Since a umaxint_t's factors must fit in FACTOR_PIPE_BUF
-         we're guaranteed to find a newline here.  */
-      char *trailing_newline = memrchr (lbuf_buf, '\n', FACTOR_PIPE_BUF);
-      char *suffix = trailing_newline + 1;
-      idx_t prefix_size = suffix - lbuf_buf;
-      idx_t suffix_size = lbuffered - prefix_size;
-
-      lbuffered = prefix_size;
-      lbuf_flush ();
-
-      /* Buffer the remainder.  */
-      lbuffered = suffix_size;
-      memcpy (lbuf_buf, suffix, suffix_size);
-    }
+    lbuf_half_flush ();
 }
 
 /* Buffer an int to the internal LBUF.  */
@@ -2422,6 +2424,33 @@ print_uintmaxes (uintmax_t t1, uintmax_t t0)
     }
 }
 
+/* Buffer an mpz to the internal LBUF, possibly writing if it is long.  */
+static void
+lbuf_putmpz (mpz_t const i)
+{
+  idx_t sizeinbase = mpz_sizeinbase (i, 10);
+  char *lbuf_bufend = lbuf_buf + sizeof lbuf_buf;
+  char *p = lbuf_buf + lbuffered;
+  if (sizeinbase < lbuf_bufend - p)
+    {
+      mpz_get_str (p, 10, i);
+      p += sizeinbase;
+      lbuffered = p - !p[-1] - lbuf_buf;
+      while (FACTOR_PIPE_BUF <= lbuffered)
+        lbuf_half_flush ();
+    }
+  else
+    {
+      lbuf_flush ();
+      char *istr = ximalloc (sizeinbase + 1);
+      mpz_get_str (istr, 10, i);
+      idx_t istrlen = sizeinbase - !istr[sizeinbase - 1];
+      if (full_write (STDOUT_FILENO, istr, istrlen) != istrlen)
+        write_error ();
+      free (istr);
+    }
+}
+
 /* Single-precision factoring */
 static void
 print_factors_single (uintmax_t t1, uintmax_t t0)
@@ -2503,26 +2532,26 @@ print_factors (char const *input)
 
   mpz_init_set_str (t, str, 10);
 
-  mpz_out_str (stdout, 10, t);
-  putchar (':');
+  lbuf_putmpz (t);
+  lbuf_putc (':');
   mp_factor (t, &factors);
 
   for (idx_t j = 0; j < factors.nfactors; j++)
     for (unsigned long int k = 0; k < factors.e[j]; k++)
       {
-        putchar (' ');
-        mpz_out_str (stdout, 10, factors.p[j]);
+        lbuf_putc (' ');
+        lbuf_putmpz (factors.p[j]);
         if (print_exponents && factors.e[j] > 1)
           {
-            printf ("^%lu", factors.e[j]);
+            lbuf_putc ('^');
+            lbuf_putint (factors.e[j], 0);
             break;
           }
       }
 
   mp_factor_clear (&factors);
   mpz_clear (t);
-  putchar ('\n');
-  fflush (stdout);
+  lbuf_putnl ();
   return true;
 }
 
@@ -2588,7 +2617,6 @@ main (int argc, char **argv)
   textdomain (PACKAGE);
 
   atexit (close_stdout);
-  atexit (lbuf_flush);
 
   int c;
   while ((c = getopt_long (argc, argv, "h", long_options, nullptr)) != -1)
@@ -2612,6 +2640,8 @@ main (int argc, char **argv)
         }
     }
 
+  atexit (lbuf_flush);
+
 #if STAT_SQUFOF
   memset (q_freq, 0, sizeof (q_freq));
 #endif
-- 
2.47.2