2 files changed, 65 insertions, 25 deletions

diff --git a/tests/seq.test b/tests/seq.test
index 15a208bb..4284617d 100755
--- a/tests/seq.test
+++ b/tests/seq.test
@@ -69,3 +69,5 @@ testing "invalid increment" "seq 1 1f 1 2>/dev/null || echo y" "y\n" "" ""
 
 # TODO: busybox fails this too, but GNU seems to not use double for large ints.
 #testing "too large for double" "seq -s, 9007199254740991 1 9007199254740992" "9007199254740992\n" "" ""
+
+testing "fast path" "timeout 10 seq 10000000 > /dev/null" "" "" ""
diff --git a/toys/lsb/seq.c b/toys/lsb/seq.c
index 988466b7..45c82d51 100644
--- a/toys/lsb/seq.c
+++ b/toys/lsb/seq.c
@@ -28,7 +28,7 @@ config SEQ
 GLOBALS(
   char *s, *f;
 
-  int precision;
+  int precision, buflen;
 )
 
 // Ensure there's one %f escape with correct attributes
@@ -37,10 +37,8 @@ static void insanitize(char *f)
   char *s = next_printf(f, 0);
 
   if (!s) error_exit("bad -f no %%f");
-  if (-1 == stridx("aAeEfFgG", *s) || (s = next_printf(s, 0))) {
-    // The @ is a byte offset, not utf8 chars. Waiting for somebody to complain.
+  if (-1 == stridx("aAeEfFgG", *s) || (s = next_printf(s, 0)))
     error_exit("bad -f '%s'@%d", f, (int)(s-f+1));
-  }
 }
 
 // Parse a numeric argument setting *prec to the precision of this argument.
@@ -54,11 +52,38 @@ static double parsef(char *s)
   return xstrtod(s);
 }
 
+// fast integer conversion to decimal string
+char *itoa(char *s, int i)
+{
+  char buf[16], *ff = buf;
+
+  if (i<0) {
+    *s++ = '-';
+    i = -i;
+  }
+  do *ff++ = '0'+i%10; while ((i /= 10));
+  do *s++ = *--ff; while (ff>buf);
+  *s++ = '\n';
+
+  return s;
+}
+
+char *flush_toybuf(char *ss)
+{
+  if (ss-toybuf<TT.buflen) return ss;
+
+  xwrite(1, toybuf, ss-toybuf); 
+
+  return toybuf;
+}
+
 void seq_main(void)
 {
+  char fbuf[32], *ss;
   double first = 1, increment = 1, last, dd;
-  int i;
+  int ii, inc = 1, len, slen;
 
+  // parse arguments
   if (!TT.s) TT.s = "\n";
   switch (toys.optc) {
     case 3: increment = parsef(toys.optargs[1]);
@@ -66,19 +91,32 @@ void seq_main(void)
     default: last = parsef(toys.optargs[toys.optc-1]);
   }
 
-  // Prepare format string with appropriate precision. Can't use %g because 1e6
-  if (toys.optflags & FLAG_f) insanitize(TT.f);
-  else sprintf(TT.f = toybuf, "%%.%df", TT.precision);
-
-  // Pad to largest width
-  if (toys.optflags & FLAG_w) {
-    int len = 0;
-
-    for (i=0; i<3; i++) {
-      dd = (double []){first, increment, last}[i];
-      len = maxof(len, snprintf(0, 0, TT.f, dd));
-    }
-    sprintf(TT.f = toybuf, "%%0%d.%df", len, TT.precision);
+  // measure arguments
+  if (FLAG(f)) insanitize(TT.f);
+  for (ii = len = 0; ii<3; ii++) {
+    dd = (double []){first, increment, last}[ii];
+    len = maxof(len, snprintf(0, 0, "%.*f", TT.precision, fabs(dd)));
+    if (ii == 2) dd += increment;
+    slen = dd;
+    if (dd != slen) inc = 0;
+  }
+  if (!FLAG(f)) sprintf(TT.f = fbuf, "%%0%d.%df", len, TT.precision);
+  TT.buflen = sizeof(toybuf) - 32 - len - TT.precision - strlen(TT.s);
+  if (TT.buflen<0) error_exit("bad -s");
+
+  // fast path: when everything fits in an int with no flags.
+  if (!toys.optflags && inc) {
+    ii = first;
+    len = last;
+    inc = increment;
+    ss = toybuf;
+    if (inc>0) for (; ii<=len; ii += inc)
+      ss = flush_toybuf(itoa(ss, ii));
+    else if (inc<0) for (; ii>=len; ii += inc)
+      ss = flush_toybuf(itoa(ss, ii));
+    if (ss != toybuf) write(1, toybuf, ss-toybuf);
+
+    return;
   }
 
   // Other implementations output nothing if increment is 0 and first > last,
@@ -86,14 +124,14 @@ void seq_main(void)
   // nothing for all three, if you want endless output use "yes".
   if (!increment) return;
 
-  i = 0;
-  for (;;) {
+  // Slow path, floating point and fancy sprintf() patterns
+  for (ii = 0, ss = toybuf;; ii++) {
     // Multiply to avoid accumulating rounding errors from increment.
-    dd = first+i*increment;
+    dd = first+ii*increment;
     if ((increment<0 && dd<last) || (increment>0 && dd>last)) break;
-    if (i++) printf("%s", TT.s);
-    printf(TT.f, dd);
+    if (ii) ss = flush_toybuf(stpcpy(ss, TT.s));
+    ss += sprintf(ss, TT.f, dd);
   }
-
-  if (i) printf("\n");
+  *ss++ = '\n';
+  xwrite(1, toybuf, ss-toybuf);
 }