bn/asm/bn-c64xplus.asm: update commentary.

Reviewed-by: Rich Salz <rsalz@openssl.org>

diff --git a/crypto/bn/asm/bn-c64xplus.asm b/crypto/bn/asm/bn-c64xplus.asm
index 7cd58817e72790b6df43bec01c5c07260922c16f..7b72bff4acda60849be7102be55bed81b1fd42d3 100644 (file)
--- a/crypto/bn/asm/bn-c64xplus.asm
+++ b/crypto/bn/asm/bn-c64xplus.asm
@@ -284,8 +284,9 @@ _bn_mul_comba4:
        .if     0
        BNOP    sploopNxM?,3
        ;; Above mentioned m*2*(n+1)+10 does not apply in n=m=4 case,
-       ;; because of read-after-write penalties, it's rather
-       ;; n*2*(n+3)+10, or 66 cycles [plus various overheads]...
+       ;; because of low-counter effect, when prologue phase finishes
+       ;; before SPKERNEL instruction is reached. As result it's 25%
+       ;; slower than expected...
        MVK     4,B0            ; N, RILC
 ||     MVK     4,A0            ; M, outer loop counter
 ||     MV      ARG1,A5         ; copy ap