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| author | Denys Vlasenko | 2021-04-20 19:01:43 +0200 |
|---|---|---|
| committer | Denys Vlasenko | 2021-04-20 19:01:43 +0200 |
| commit | 21367b283909cb71ef74cb0e89f77334e9eb6a61 (patch) | |
| tree | f7880497fcebaa1f003811dfe8320e7110bee362 | |
| parent | f277c9eebb91a46cbd795c34aa64ee8b6a2e448c (diff) | |
| download | busybox-21367b283909cb71ef74cb0e89f77334e9eb6a61.zip busybox-21367b283909cb71ef74cb0e89f77334e9eb6a61.tar.gz | |
tls: reduce register pressure in i386 assembly (helps Android to compile)
function old new delta
pstm_montgomery_reduce 440 435 -5
Signed-off-by: Denys Vlasenko <vda.linux@googlemail.com>
| -rw-r--r-- | networking/tls_pstm_montgomery_reduce.c | 24 |
1 files changed, 24 insertions, 0 deletions
diff --git a/networking/tls_pstm_montgomery_reduce.c b/networking/tls_pstm_montgomery_reduce.c index 20f9c26..e8857f3 100644 --- a/networking/tls_pstm_montgomery_reduce.c +++ b/networking/tls_pstm_montgomery_reduce.c @@ -62,6 +62,7 @@ #define LOOP_START \ mu = c[x] * mp +#if 0 #define INNERMUL \ asm( \ "movl %5,%%eax \n\t" \ @@ -74,6 +75,29 @@ asm( \ :"=g"(_c[LO]), "=r"(cy) \ :"0"(_c[LO]), "1"(cy), "g"(mu), "g"(*tmpm++) \ : "%eax", "%edx", "cc") +/* + * The above generated "error: 'asm' operand has impossible constraints" on Android. + * Do they reserve in their ABI a register for something, and there aren't enough left? + */ +#else +/* Let's avoid two explicit "movl" by telling compiler to put input value of *tmpm++ + * into EAX, and to expect cy result in EDX: + */ +#define INNERMUL \ +asm( \ + "mull %4 \n\t" \ + "addl %3,%%eax \n\t" \ + "adcl $0,%%edx \n\t" \ + "addl %%eax,%0 \n\t" \ + "adcl $0,%%edx \n\t" \ +:"=g"(_c[LO]), "=&d"(cy) \ +:"0"(_c[LO]), "g"(cy), "g"(mu), "a"(*tmpm++) \ +:"cc") +/* This doesn't tell compiler that we clobber EAX, but it probably won't need + * the value of *tmpm anyway, thus won't try to reuse EAX contents. + * TODO: fix it with dummy "=a"(clobbered_eax) output? + */ +#endif #define PROPCARRY \ asm( \ |