Show millisecond precision for time_passes times

Closes #713

Author: marijnh

src/comp/driver/rustc.rs

@@ -99,12 +99,11 @@ fn parse_input(sess: session::session, cfg: &ast::crate_cfg, input: str) ->
 
 fn time[T](do_it: bool, what: str, thunk: fn() -> T ) -> T {
     if !do_it { ret thunk(); }
-    let start = std::time::get_time();
+    let start = std::time::precise_time_s();
     let rv = thunk();
-    let end = std::time::get_time();
-    // FIXME: Actually do timeval math.
-
-    log_err #fmt("time: %s took %u s", what, end.sec - start.sec as uint);
+    let end = std::time::precise_time_s();
+    log_err #fmt("time: %s took %s s", what,
+                 common::float_to_str(end - start, 3u));
     ret rv;
 }
 

src/comp/util/common.rs

@@ -163,6 +163,28 @@ fn call_kind_str(c: call_kind) -> str {
 fn is_main_name(path: &str[]) -> bool {
     str::eq(option::get(std::ivec::last(path)), "main")
 }
+
+// FIXME mode this to std::float when editing the stdlib no longer
+// requires a snapshot
+fn float_to_str(num: float, digits: uint) -> str {
+    let accum = if num < 0.0 { num = -num; "-" }
+                else { "" };
+    let trunc = num as uint;
+    let frac = num - (trunc as float);
+    accum += uint::str(trunc);
+    if frac == 0.0 || digits == 0u { ret accum; }
+    accum += ".";
+    while digits > 0u && frac > 0.0 {
+        frac *= 10.0;
+        let digit = frac as uint;
+        accum += uint::str(digit);
+        frac -= digit as float;
+        digits -= 1u;
+    }
+    ret accum;
+}
+
+
 //
 // Local Variables:
 // mode: rust