diff options
| author | Aurelien Jarno <aurelien@aurel32.net> | 2015-07-05 18:50:09 +0200 |
|---|---|---|
| committer | Aurelien Jarno <aurelien@aurel32.net> | 2015-09-13 23:08:51 +0200 |
| commit | eb6ca2b4a69325e95526bc0f2897791df04e44dc (patch) | |
| tree | 1501d1dabef3ec5639070bec1ad1bd54deb8d3a5 /target-sh4/translate.c | |
| parent | 218fd7301f88df440da3e16b9cfca000cd2fe111 (diff) | |
target-sh4: improve cmp/str instruction
Instead of testing bytes one by one, we can use the following trick
from https://graphics.stanford.edu/~seander/bithacks.html:
haszero(v) = (v - 0x01010101) & ~v & 0x80808080
The subexpression v - 0x01010101, evaluates to a high bit set in any
byte whenever the corresponding byte in v is zero or greater than 0x80.
The sub-expression ~v & 0x80808080 evaluates to high bits set in bytes
where the byte of v doesn't have its high bit set (so the byte was less
than 0x80). Finally, by ANDing these two sub-expressions the result is
the high bits set where the bytes in v were zero, since the high bits
set due to a value greater than 0x80 in the first sub-expression are
masked off by the second.
Reviewed-by: Richard Henderson <rth@twiddle.net>
Signed-off-by: Aurelien Jarno <aurelien@aurel32.net>
Diffstat (limited to 'target-sh4/translate.c')
| -rw-r--r-- | target-sh4/translate.c | 17 |
1 files changed, 5 insertions, 12 deletions
diff --git a/target-sh4/translate.c b/target-sh4/translate.c index 50043cf5b5..ca6ef5aca7 100644 --- a/target-sh4/translate.c +++ b/target-sh4/translate.c @@ -688,18 +688,11 @@ static void _decode_opc(DisasContext * ctx) { TCGv cmp1 = tcg_temp_new(); TCGv cmp2 = tcg_temp_new(); - tcg_gen_xor_i32(cmp1, REG(B7_4), REG(B11_8)); - tcg_gen_andi_i32(cmp2, cmp1, 0xff000000); - tcg_gen_setcondi_i32(TCG_COND_EQ, cpu_sr_t, cmp2, 0); - tcg_gen_andi_i32(cmp2, cmp1, 0x00ff0000); - tcg_gen_setcondi_i32(TCG_COND_EQ, cmp2, cmp2, 0); - tcg_gen_or_i32(cpu_sr_t, cpu_sr_t, cmp2); - tcg_gen_andi_i32(cmp2, cmp1, 0x0000ff00); - tcg_gen_setcondi_i32(TCG_COND_EQ, cmp2, cmp2, 0); - tcg_gen_or_i32(cpu_sr_t, cpu_sr_t, cmp2); - tcg_gen_andi_i32(cmp2, cmp1, 0x000000ff); - tcg_gen_setcondi_i32(TCG_COND_EQ, cmp2, cmp2, 0); - tcg_gen_or_i32(cpu_sr_t, cpu_sr_t, cmp2); + tcg_gen_xor_i32(cmp2, REG(B7_4), REG(B11_8)); + tcg_gen_subi_i32(cmp1, cmp2, 0x01010101); + tcg_gen_andc_i32(cmp1, cmp1, cmp2); + tcg_gen_andi_i32(cmp1, cmp1, 0x80808080); + tcg_gen_setcondi_i32(TCG_COND_NE, cpu_sr_t, cmp1, 0); tcg_temp_free(cmp2); tcg_temp_free(cmp1); } |