4/4] target-ppc: Implement bcdctz. instruction
diff mbox

Message ID 1477487938-23921-5-git-send-email-joserz@linux.vnet.ibm.com
State New
Headers show

Commit Message

Jose Ricardo Ziviani Oct. 26, 2016, 1:18 p.m. UTC
bcdctz. converts from BCD to Zoned numeric format. Zoned format uses
a byte to represent a digit where the most significant nibble is 0x3
or 0xf, depending on the preferred signal.

Signed-off-by: Jose Ricardo Ziviani <joserz@linux.vnet.ibm.com>
---
 target-ppc/helper.h                 |  1 +
 target-ppc/int_helper.c             | 54 +++++++++++++++++++++++++++++++++++++
 target-ppc/translate/vmx-impl.inc.c |  7 +++--
 3 files changed, 60 insertions(+), 2 deletions(-)

Comments

David Gibson Oct. 27, 2016, 1:47 a.m. UTC | #1
On Wed, Oct 26, 2016 at 11:18:58AM -0200, Jose Ricardo Ziviani wrote:
> bcdctz. converts from BCD to Zoned numeric format. Zoned format uses
> a byte to represent a digit where the most significant nibble is 0x3
> or 0xf, depending on the preferred signal.
> 
> Signed-off-by: Jose Ricardo Ziviani <joserz@linux.vnet.ibm.com>
> ---
>  target-ppc/helper.h                 |  1 +
>  target-ppc/int_helper.c             | 54 +++++++++++++++++++++++++++++++++++++
>  target-ppc/translate/vmx-impl.inc.c |  7 +++--
>  3 files changed, 60 insertions(+), 2 deletions(-)
> 
> diff --git a/target-ppc/helper.h b/target-ppc/helper.h
> index f460635..3b928b8 100644
> --- a/target-ppc/helper.h
> +++ b/target-ppc/helper.h
> @@ -372,6 +372,7 @@ DEF_HELPER_4(bcdsub, i32, avr, avr, avr, i32)
>  DEF_HELPER_3(bcdcfn, i32, avr, avr, i32)
>  DEF_HELPER_2(bcdctn, i32, avr, avr)
>  DEF_HELPER_3(bcdcfz, i32, avr, avr, i32)
> +DEF_HELPER_3(bcdctz, i32, avr, avr, i32)
>  
>  DEF_HELPER_2(xsadddp, void, env, i32)
>  DEF_HELPER_2(xssubdp, void, env, i32)
> diff --git a/target-ppc/int_helper.c b/target-ppc/int_helper.c
> index 8cbbdfc..e0a84bb 100644
> --- a/target-ppc/int_helper.c
> +++ b/target-ppc/int_helper.c
> @@ -2768,6 +2768,60 @@ uint32_t helper_bcdcfz(ppc_avr_t *r, ppc_avr_t *b, uint32_t ps)
>      *r = ret;
>      return cr;
>  }
> +
> +uint32_t helper_bcdctz(ppc_avr_t *r, ppc_avr_t *b, uint32_t ps)
> +{
> +    int i;
> +    int j;
> +    int cr = 0;
> +    int invalid = 0;
> +    uint8_t digit = 0;
> +    int sgnb = bcd_get_sgn(b);
> +    int zone_lead = (ps) ? 0xF0 : 0x30;
> +    ppc_avr_t ret = { .u64 = { 0, 0 } };
> +
> +    int eq_flag = (b->u64[HI_IDX] == 0) && ((b->u64[LO_IDX] >> 4) == 0);
> +    int ox_flag = (b->u64[HI_IDX] != 0);

This doesn't look right.  The zoned format can accomodate 16 digits.
The low word of the packed format can accomodate 15 digits + sign.  So
it should be possible to convert a packed for with a value in the low
nibble of the upper word.

> +    for (i = 31, j = 16; i > 1; i -= 2, j--) {

Again not seeing any point for the reverse order.

> +        digit = get_nibble(b, j);
> +        ret.u8[BCD_DIG_BYTE(i)] = zone_lead + digit;
> +
> +        if (unlikely(digit > 9)) {
> +            invalid = 1;
> +        }
> +    }
> +
> +    if (unlikely(!sgnb)) {
> +        sgnb = (!get_nibble(b, 0)) ? 1 : -1;
> +    }

Doesn't bcd_get_sgn() returning 0 indicate a badly encoded sign
point.  In which case you should set invalid, rather than making up a
sign according to this apparently arbitrary scheme.

> +
> +    if (ps) {
> +        bcd_put_digit(&ret, (sgnb == 1) ? 0xC : 0xD, 1);
> +    } else {
> +        bcd_put_digit(&ret, (sgnb == 1) ? 0x3 : 0x7, 1);
> +    }
> +    bcd_put_digit(&ret, get_nibble(b, 1), 0);
> +
> +    if (!eq_flag) {
> +        cr = (sgnb == 1) ? 1 << CRF_GT : 1 << CRF_LT;
> +    } else {
> +        cr = 1 << CRF_EQ;
> +    }
> +
> +    if (ox_flag) {
> +        cr |= 1 << CRF_SO;
> +    }
> +
> +    if (unlikely(invalid)) {
> +        cr = 1 << CRF_SO;
> +    }
> +
> +    *r = ret;
> +
> +    return cr;
> +}
> +
>  void helper_vsbox(ppc_avr_t *r, ppc_avr_t *a)
>  {
>      int i;
> diff --git a/target-ppc/translate/vmx-impl.inc.c b/target-ppc/translate/vmx-impl.inc.c
> index 9192f8f..62c44f0 100644
> --- a/target-ppc/translate/vmx-impl.inc.c
> +++ b/target-ppc/translate/vmx-impl.inc.c
> @@ -918,6 +918,7 @@ GEN_BCD(bcdsub)
>  GEN_BCD2(bcdcfn)
>  GEN_BCD3(bcdctn)
>  GEN_BCD2(bcdcfz)
> +GEN_BCD2(bcdctz)
>  
>  static void gen_xpnd04_1(DisasContext *ctx)
>  {
> @@ -927,7 +928,8 @@ static void gen_xpnd04_1(DisasContext *ctx)
>      case 2:
>          break; /* bcdcfsq. */
>      case 4:
> -        break; /* bcdctz. */
> +        gen_bcdctz(ctx);
> +        break;
>      case 5:
>          gen_bcdctn(ctx);
>          break;
> @@ -952,7 +954,8 @@ static void gen_xpnd04_2(DisasContext *ctx)
>      case 2:
>          break; /* bcdcfsq. */
>      case 4:
> -        break; /* bcdctz. */
> +        gen_bcdctz(ctx);
> +        break;
>      case 6:
>          gen_bcdcfz(ctx);
>          break;
Jose Ricardo Ziviani Oct. 27, 2016, 6:29 p.m. UTC | #2
Everything will be fixed in v2.

Thanks for reviewing it!

On Thu, Oct 27, 2016 at 12:47:34PM +1100, David Gibson wrote:
> On Wed, Oct 26, 2016 at 11:18:58AM -0200, Jose Ricardo Ziviani wrote:
> > bcdctz. converts from BCD to Zoned numeric format. Zoned format uses
> > a byte to represent a digit where the most significant nibble is 0x3
> > or 0xf, depending on the preferred signal.
> > 
> > Signed-off-by: Jose Ricardo Ziviani <joserz@linux.vnet.ibm.com>
> > ---
> >  target-ppc/helper.h                 |  1 +
> >  target-ppc/int_helper.c             | 54 +++++++++++++++++++++++++++++++++++++
> >  target-ppc/translate/vmx-impl.inc.c |  7 +++--
> >  3 files changed, 60 insertions(+), 2 deletions(-)
> > 
> > diff --git a/target-ppc/helper.h b/target-ppc/helper.h
> > index f460635..3b928b8 100644
> > --- a/target-ppc/helper.h
> > +++ b/target-ppc/helper.h
> > @@ -372,6 +372,7 @@ DEF_HELPER_4(bcdsub, i32, avr, avr, avr, i32)
> >  DEF_HELPER_3(bcdcfn, i32, avr, avr, i32)
> >  DEF_HELPER_2(bcdctn, i32, avr, avr)
> >  DEF_HELPER_3(bcdcfz, i32, avr, avr, i32)
> > +DEF_HELPER_3(bcdctz, i32, avr, avr, i32)
> >  
> >  DEF_HELPER_2(xsadddp, void, env, i32)
> >  DEF_HELPER_2(xssubdp, void, env, i32)
> > diff --git a/target-ppc/int_helper.c b/target-ppc/int_helper.c
> > index 8cbbdfc..e0a84bb 100644
> > --- a/target-ppc/int_helper.c
> > +++ b/target-ppc/int_helper.c
> > @@ -2768,6 +2768,60 @@ uint32_t helper_bcdcfz(ppc_avr_t *r, ppc_avr_t *b, uint32_t ps)
> >      *r = ret;
> >      return cr;
> >  }
> > +
> > +uint32_t helper_bcdctz(ppc_avr_t *r, ppc_avr_t *b, uint32_t ps)
> > +{
> > +    int i;
> > +    int j;
> > +    int cr = 0;
> > +    int invalid = 0;
> > +    uint8_t digit = 0;
> > +    int sgnb = bcd_get_sgn(b);
> > +    int zone_lead = (ps) ? 0xF0 : 0x30;
> > +    ppc_avr_t ret = { .u64 = { 0, 0 } };
> > +
> > +    int eq_flag = (b->u64[HI_IDX] == 0) && ((b->u64[LO_IDX] >> 4) == 0);
> > +    int ox_flag = (b->u64[HI_IDX] != 0);
> 
> This doesn't look right.  The zoned format can accomodate 16 digits.
> The low word of the packed format can accomodate 15 digits + sign.  So
> it should be possible to convert a packed for with a value in the low
> nibble of the upper word.
> 
> > +    for (i = 31, j = 16; i > 1; i -= 2, j--) {
> 
> Again not seeing any point for the reverse order.
> 
> > +        digit = get_nibble(b, j);
> > +        ret.u8[BCD_DIG_BYTE(i)] = zone_lead + digit;
> > +
> > +        if (unlikely(digit > 9)) {
> > +            invalid = 1;
> > +        }
> > +    }
> > +
> > +    if (unlikely(!sgnb)) {
> > +        sgnb = (!get_nibble(b, 0)) ? 1 : -1;
> > +    }
> 
> Doesn't bcd_get_sgn() returning 0 indicate a badly encoded sign
> point.  In which case you should set invalid, rather than making up a
> sign according to this apparently arbitrary scheme.
> 
> > +
> > +    if (ps) {
> > +        bcd_put_digit(&ret, (sgnb == 1) ? 0xC : 0xD, 1);
> > +    } else {
> > +        bcd_put_digit(&ret, (sgnb == 1) ? 0x3 : 0x7, 1);
> > +    }
> > +    bcd_put_digit(&ret, get_nibble(b, 1), 0);
> > +
> > +    if (!eq_flag) {
> > +        cr = (sgnb == 1) ? 1 << CRF_GT : 1 << CRF_LT;
> > +    } else {
> > +        cr = 1 << CRF_EQ;
> > +    }
> > +
> > +    if (ox_flag) {
> > +        cr |= 1 << CRF_SO;
> > +    }
> > +
> > +    if (unlikely(invalid)) {
> > +        cr = 1 << CRF_SO;
> > +    }
> > +
> > +    *r = ret;
> > +
> > +    return cr;
> > +}
> > +
> >  void helper_vsbox(ppc_avr_t *r, ppc_avr_t *a)
> >  {
> >      int i;
> > diff --git a/target-ppc/translate/vmx-impl.inc.c b/target-ppc/translate/vmx-impl.inc.c
> > index 9192f8f..62c44f0 100644
> > --- a/target-ppc/translate/vmx-impl.inc.c
> > +++ b/target-ppc/translate/vmx-impl.inc.c
> > @@ -918,6 +918,7 @@ GEN_BCD(bcdsub)
> >  GEN_BCD2(bcdcfn)
> >  GEN_BCD3(bcdctn)
> >  GEN_BCD2(bcdcfz)
> > +GEN_BCD2(bcdctz)
> >  
> >  static void gen_xpnd04_1(DisasContext *ctx)
> >  {
> > @@ -927,7 +928,8 @@ static void gen_xpnd04_1(DisasContext *ctx)
> >      case 2:
> >          break; /* bcdcfsq. */
> >      case 4:
> > -        break; /* bcdctz. */
> > +        gen_bcdctz(ctx);
> > +        break;
> >      case 5:
> >          gen_bcdctn(ctx);
> >          break;
> > @@ -952,7 +954,8 @@ static void gen_xpnd04_2(DisasContext *ctx)
> >      case 2:
> >          break; /* bcdcfsq. */
> >      case 4:
> > -        break; /* bcdctz. */
> > +        gen_bcdctz(ctx);
> > +        break;
> >      case 6:
> >          gen_bcdcfz(ctx);
> >          break;
> 
> -- 
> David Gibson			| I'll have my music baroque, and my code
> david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
> 				| _way_ _around_!
> http://www.ozlabs.org/~dgibson
Jose Ricardo Ziviani Oct. 27, 2016, 8:08 p.m. UTC | #3
On Thu, Oct 27, 2016 at 12:47:34PM +1100, David Gibson wrote:
> On Wed, Oct 26, 2016 at 11:18:58AM -0200, Jose Ricardo Ziviani wrote:
> > bcdctz. converts from BCD to Zoned numeric format. Zoned format uses
> > a byte to represent a digit where the most significant nibble is 0x3
> > or 0xf, depending on the preferred signal.
> > 
> > Signed-off-by: Jose Ricardo Ziviani <joserz@linux.vnet.ibm.com>
> > ---
> >  target-ppc/helper.h                 |  1 +
> >  target-ppc/int_helper.c             | 54 +++++++++++++++++++++++++++++++++++++
> >  target-ppc/translate/vmx-impl.inc.c |  7 +++--
> >  3 files changed, 60 insertions(+), 2 deletions(-)
> > 
> > diff --git a/target-ppc/helper.h b/target-ppc/helper.h
> > index f460635..3b928b8 100644
> > --- a/target-ppc/helper.h
> > +++ b/target-ppc/helper.h
> > @@ -372,6 +372,7 @@ DEF_HELPER_4(bcdsub, i32, avr, avr, avr, i32)
> >  DEF_HELPER_3(bcdcfn, i32, avr, avr, i32)
> >  DEF_HELPER_2(bcdctn, i32, avr, avr)
> >  DEF_HELPER_3(bcdcfz, i32, avr, avr, i32)
> > +DEF_HELPER_3(bcdctz, i32, avr, avr, i32)
> >  
> >  DEF_HELPER_2(xsadddp, void, env, i32)
> >  DEF_HELPER_2(xssubdp, void, env, i32)
> > diff --git a/target-ppc/int_helper.c b/target-ppc/int_helper.c
> > index 8cbbdfc..e0a84bb 100644
> > --- a/target-ppc/int_helper.c
> > +++ b/target-ppc/int_helper.c
> > @@ -2768,6 +2768,60 @@ uint32_t helper_bcdcfz(ppc_avr_t *r, ppc_avr_t *b, uint32_t ps)
> >      *r = ret;
> >      return cr;
> >  }
> > +
> > +uint32_t helper_bcdctz(ppc_avr_t *r, ppc_avr_t *b, uint32_t ps)
> > +{
> > +    int i;
> > +    int j;
> > +    int cr = 0;
> > +    int invalid = 0;
> > +    uint8_t digit = 0;
> > +    int sgnb = bcd_get_sgn(b);
> > +    int zone_lead = (ps) ? 0xF0 : 0x30;
> > +    ppc_avr_t ret = { .u64 = { 0, 0 } };
> > +
> > +    int eq_flag = (b->u64[HI_IDX] == 0) && ((b->u64[LO_IDX] >> 4) == 0);
> > +    int ox_flag = (b->u64[HI_IDX] != 0);
> 
> This doesn't look right.  The zoned format can accomodate 16 digits.
> The low word of the packed format can accomodate 15 digits + sign.  So
> it should be possible to convert a packed for with a value in the low
> nibble of the upper word.

David, it seems that zoned format can accommodate 15 digits + sign at most. Suppose I have this 16 bytes zoned number: f9f9f9f9f9f9f9f9f9f9f9f9f9f9f9xx. Converting it to packed bcd will give 999999999999999x. Do you agree? can I keep that ox_flag logic?

> 
> > +    for (i = 31, j = 16; i > 1; i -= 2, j--) {
> 
> Again not seeing any point for the reverse order.
> 
> > +        digit = get_nibble(b, j);
> > +        ret.u8[BCD_DIG_BYTE(i)] = zone_lead + digit;
> > +
> > +        if (unlikely(digit > 9)) {
> > +            invalid = 1;
> > +        }
> > +    }
> > +
> > +    if (unlikely(!sgnb)) {
> > +        sgnb = (!get_nibble(b, 0)) ? 1 : -1;
> > +    }
> 
> Doesn't bcd_get_sgn() returning 0 indicate a badly encoded sign
> point.  In which case you should set invalid, rather than making up a
> sign according to this apparently arbitrary scheme.
> 
> > +
> > +    if (ps) {
> > +        bcd_put_digit(&ret, (sgnb == 1) ? 0xC : 0xD, 1);
> > +    } else {
> > +        bcd_put_digit(&ret, (sgnb == 1) ? 0x3 : 0x7, 1);
> > +    }
> > +    bcd_put_digit(&ret, get_nibble(b, 1), 0);
> > +
> > +    if (!eq_flag) {
> > +        cr = (sgnb == 1) ? 1 << CRF_GT : 1 << CRF_LT;
> > +    } else {
> > +        cr = 1 << CRF_EQ;
> > +    }
> > +
> > +    if (ox_flag) {
> > +        cr |= 1 << CRF_SO;
> > +    }
> > +
> > +    if (unlikely(invalid)) {
> > +        cr = 1 << CRF_SO;
> > +    }
> > +
> > +    *r = ret;
> > +
> > +    return cr;
> > +}
> > +
> >  void helper_vsbox(ppc_avr_t *r, ppc_avr_t *a)
> >  {
> >      int i;
> > diff --git a/target-ppc/translate/vmx-impl.inc.c b/target-ppc/translate/vmx-impl.inc.c
> > index 9192f8f..62c44f0 100644
> > --- a/target-ppc/translate/vmx-impl.inc.c
> > +++ b/target-ppc/translate/vmx-impl.inc.c
> > @@ -918,6 +918,7 @@ GEN_BCD(bcdsub)
> >  GEN_BCD2(bcdcfn)
> >  GEN_BCD3(bcdctn)
> >  GEN_BCD2(bcdcfz)
> > +GEN_BCD2(bcdctz)
> >  
> >  static void gen_xpnd04_1(DisasContext *ctx)
> >  {
> > @@ -927,7 +928,8 @@ static void gen_xpnd04_1(DisasContext *ctx)
> >      case 2:
> >          break; /* bcdcfsq. */
> >      case 4:
> > -        break; /* bcdctz. */
> > +        gen_bcdctz(ctx);
> > +        break;
> >      case 5:
> >          gen_bcdctn(ctx);
> >          break;
> > @@ -952,7 +954,8 @@ static void gen_xpnd04_2(DisasContext *ctx)
> >      case 2:
> >          break; /* bcdcfsq. */
> >      case 4:
> > -        break; /* bcdctz. */
> > +        gen_bcdctz(ctx);
> > +        break;
> >      case 6:
> >          gen_bcdcfz(ctx);
> >          break;
> 
> -- 
> David Gibson			| I'll have my music baroque, and my code
> david AT gibson.dropbear.id.au	| minimalist, thank you.  NOT _the_ _other_
> 				| _way_ _around_!
> http://www.ozlabs.org/~dgibson
David Gibson Oct. 31, 2016, 2:50 a.m. UTC | #4
On Thu, Oct 27, 2016 at 06:08:20PM -0200, joserz@linux.vnet.ibm.com wrote:
> On Thu, Oct 27, 2016 at 12:47:34PM +1100, David Gibson wrote:
> > On Wed, Oct 26, 2016 at 11:18:58AM -0200, Jose Ricardo Ziviani wrote:
> > > bcdctz. converts from BCD to Zoned numeric format. Zoned format uses
> > > a byte to represent a digit where the most significant nibble is 0x3
> > > or 0xf, depending on the preferred signal.
> > > 
> > > Signed-off-by: Jose Ricardo Ziviani <joserz@linux.vnet.ibm.com>
> > > ---
> > >  target-ppc/helper.h                 |  1 +
> > >  target-ppc/int_helper.c             | 54 +++++++++++++++++++++++++++++++++++++
> > >  target-ppc/translate/vmx-impl.inc.c |  7 +++--
> > >  3 files changed, 60 insertions(+), 2 deletions(-)
> > > 
> > > diff --git a/target-ppc/helper.h b/target-ppc/helper.h
> > > index f460635..3b928b8 100644
> > > --- a/target-ppc/helper.h
> > > +++ b/target-ppc/helper.h
> > > @@ -372,6 +372,7 @@ DEF_HELPER_4(bcdsub, i32, avr, avr, avr, i32)
> > >  DEF_HELPER_3(bcdcfn, i32, avr, avr, i32)
> > >  DEF_HELPER_2(bcdctn, i32, avr, avr)
> > >  DEF_HELPER_3(bcdcfz, i32, avr, avr, i32)
> > > +DEF_HELPER_3(bcdctz, i32, avr, avr, i32)
> > >  
> > >  DEF_HELPER_2(xsadddp, void, env, i32)
> > >  DEF_HELPER_2(xssubdp, void, env, i32)
> > > diff --git a/target-ppc/int_helper.c b/target-ppc/int_helper.c
> > > index 8cbbdfc..e0a84bb 100644
> > > --- a/target-ppc/int_helper.c
> > > +++ b/target-ppc/int_helper.c
> > > @@ -2768,6 +2768,60 @@ uint32_t helper_bcdcfz(ppc_avr_t *r, ppc_avr_t *b, uint32_t ps)
> > >      *r = ret;
> > >      return cr;
> > >  }
> > > +
> > > +uint32_t helper_bcdctz(ppc_avr_t *r, ppc_avr_t *b, uint32_t ps)
> > > +{
> > > +    int i;
> > > +    int j;
> > > +    int cr = 0;
> > > +    int invalid = 0;
> > > +    uint8_t digit = 0;
> > > +    int sgnb = bcd_get_sgn(b);
> > > +    int zone_lead = (ps) ? 0xF0 : 0x30;
> > > +    ppc_avr_t ret = { .u64 = { 0, 0 } };
> > > +
> > > +    int eq_flag = (b->u64[HI_IDX] == 0) && ((b->u64[LO_IDX] >> 4) == 0);
> > > +    int ox_flag = (b->u64[HI_IDX] != 0);
> > 
> > This doesn't look right.  The zoned format can accomodate 16 digits.
> > The low word of the packed format can accomodate 15 digits + sign.  So
> > it should be possible to convert a packed for with a value in the low
> > nibble of the upper word.
> 
> David, it seems that zoned format can accommodate 15 digits + sign
> at most. Suppose I have this 16 bytes zoned number:
> f9f9f9f9f9f9f9f9f9f9f9f9f9f9f9xx. Converting it to packed bcd will
> give 999999999999999x. Do you agree? can I keep that ox_flag logic?

Uh.. no.  AFAICT from the description of the instruction the last byte
of a zoned number contains *both* a sign nibble *and* the least
significant digit of the number.  So zoned format can represent 16
digits + sign.

But IIRC you changed this in v2, so maybe you realised that already.

Patch
diff mbox

diff --git a/target-ppc/helper.h b/target-ppc/helper.h
index f460635..3b928b8 100644
--- a/target-ppc/helper.h
+++ b/target-ppc/helper.h
@@ -372,6 +372,7 @@  DEF_HELPER_4(bcdsub, i32, avr, avr, avr, i32)
 DEF_HELPER_3(bcdcfn, i32, avr, avr, i32)
 DEF_HELPER_2(bcdctn, i32, avr, avr)
 DEF_HELPER_3(bcdcfz, i32, avr, avr, i32)
+DEF_HELPER_3(bcdctz, i32, avr, avr, i32)
 
 DEF_HELPER_2(xsadddp, void, env, i32)
 DEF_HELPER_2(xssubdp, void, env, i32)
diff --git a/target-ppc/int_helper.c b/target-ppc/int_helper.c
index 8cbbdfc..e0a84bb 100644
--- a/target-ppc/int_helper.c
+++ b/target-ppc/int_helper.c
@@ -2768,6 +2768,60 @@  uint32_t helper_bcdcfz(ppc_avr_t *r, ppc_avr_t *b, uint32_t ps)
     *r = ret;
     return cr;
 }
+
+uint32_t helper_bcdctz(ppc_avr_t *r, ppc_avr_t *b, uint32_t ps)
+{
+    int i;
+    int j;
+    int cr = 0;
+    int invalid = 0;
+    uint8_t digit = 0;
+    int sgnb = bcd_get_sgn(b);
+    int zone_lead = (ps) ? 0xF0 : 0x30;
+    ppc_avr_t ret = { .u64 = { 0, 0 } };
+
+    int eq_flag = (b->u64[HI_IDX] == 0) && ((b->u64[LO_IDX] >> 4) == 0);
+    int ox_flag = (b->u64[HI_IDX] != 0);
+
+    for (i = 31, j = 16; i > 1; i -= 2, j--) {
+        digit = get_nibble(b, j);
+        ret.u8[BCD_DIG_BYTE(i)] = zone_lead + digit;
+
+        if (unlikely(digit > 9)) {
+            invalid = 1;
+        }
+    }
+
+    if (unlikely(!sgnb)) {
+        sgnb = (!get_nibble(b, 0)) ? 1 : -1;
+    }
+
+    if (ps) {
+        bcd_put_digit(&ret, (sgnb == 1) ? 0xC : 0xD, 1);
+    } else {
+        bcd_put_digit(&ret, (sgnb == 1) ? 0x3 : 0x7, 1);
+    }
+    bcd_put_digit(&ret, get_nibble(b, 1), 0);
+
+    if (!eq_flag) {
+        cr = (sgnb == 1) ? 1 << CRF_GT : 1 << CRF_LT;
+    } else {
+        cr = 1 << CRF_EQ;
+    }
+
+    if (ox_flag) {
+        cr |= 1 << CRF_SO;
+    }
+
+    if (unlikely(invalid)) {
+        cr = 1 << CRF_SO;
+    }
+
+    *r = ret;
+
+    return cr;
+}
+
 void helper_vsbox(ppc_avr_t *r, ppc_avr_t *a)
 {
     int i;
diff --git a/target-ppc/translate/vmx-impl.inc.c b/target-ppc/translate/vmx-impl.inc.c
index 9192f8f..62c44f0 100644
--- a/target-ppc/translate/vmx-impl.inc.c
+++ b/target-ppc/translate/vmx-impl.inc.c
@@ -918,6 +918,7 @@  GEN_BCD(bcdsub)
 GEN_BCD2(bcdcfn)
 GEN_BCD3(bcdctn)
 GEN_BCD2(bcdcfz)
+GEN_BCD2(bcdctz)
 
 static void gen_xpnd04_1(DisasContext *ctx)
 {
@@ -927,7 +928,8 @@  static void gen_xpnd04_1(DisasContext *ctx)
     case 2:
         break; /* bcdcfsq. */
     case 4:
-        break; /* bcdctz. */
+        gen_bcdctz(ctx);
+        break;
     case 5:
         gen_bcdctn(ctx);
         break;
@@ -952,7 +954,8 @@  static void gen_xpnd04_2(DisasContext *ctx)
     case 2:
         break; /* bcdcfsq. */
     case 4:
-        break; /* bcdctz. */
+        gen_bcdctz(ctx);
+        break;
     case 6:
         gen_bcdcfz(ctx);
         break;