PRECISE_I32_MUL option for full precision in 32-bit multiply

1 files changed, 6 insertions, 1 deletions

diff --git a/emcc b/emcc
index 07cf94d1..bb1a2496 100755
--- a/emcc
+++ b/emcc
@@ -140,7 +140,12 @@ Options that are modified or new in %s include:
                            optimizations, and no runtime assertions
                            or C++ exception catching (to re-enable
                            C++ exception catching, use
-                           -s DISABLE_EXCEPTION_CATCHING=0 ).
+                           -s DISABLE_EXCEPTION_CATCHING=0 ). 32-bit
+                           multiplication is done in JS doubles which
+                           is fast but imprecise for high values.
+                           (For details on the affects of different
+                           opt levels, see apply_opt_level() in
+                           tools/shared.py)
                            Note: Optimizations are only done when
                            compiling to JavaScript, not to intermediate
                            bitcode.