diff options
| author | Austin Clements <austin@google.com> | 2014-10-31 13:39:36 -0400 |
|---|---|---|
| committer | Austin Clements <austin@google.com> | 2014-10-31 13:39:36 -0400 |
| commit | 515641a7d9e906e27c64aeb674609b55b4b43b8b (patch) | |
| tree | cccd1568501e3c91a926bf0348da455c2f7e3155 | |
| parent | bfab3e583ce8e78b9488fdb292f3f371949757a6 (diff) | |
| download | go-515641a7d9e906e27c64aeb674609b55b4b43b8b.tar.gz | |
[dev.power64] runtime: fix fastrand1 on power64x
fastrand1 depends on testing the high bit of its uint32 state.
For efficiency, all of the architectures implement this as a
sign bit test. However, on power64, fastrand1 was using a
64-bit sign test on the zero-extended 32-bit state. This
always failed, causing fastrand1 to have very short periods
and often decay to 0 and get stuck.
Fix this by using a 32-bit signed compare instead of a 64-bit
compare. This fixes various tests for the randomization of
select of map iteration.
LGTM=rsc
R=rsc, dave
CC=golang-codereviews
https://codereview.appspot.com/166990043
| -rw-r--r-- | src/runtime/asm_power64x.s | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/src/runtime/asm_power64x.s b/src/runtime/asm_power64x.s index 2ad3e56e9..713cc5f54 100644 --- a/src/runtime/asm_power64x.s +++ b/src/runtime/asm_power64x.s @@ -965,7 +965,7 @@ TEXT runtime·fastrand1(SB), NOSPLIT, $0-4 MOVD g_m(g), R4 MOVWZ m_fastrand(R4), R3 ADD R3, R3 - CMP R3, $0 + CMPW R3, $0 BGE 2(PC) XOR $0x88888eef, R3 MOVW R3, m_fastrand(R4) |