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[cff] Implement in-house power of 10 

A minimal power only for natural numbers exponents of ten, for portability.

Found the idea in Tcl/Tk but wrote it myself after weeks and it turned out
being a different implementation, reverse direction, constexpr, etc.
This commit is contained in:
Ebrahim Byagowi 2019-09-01 14:05:16 +04:30 committed by GitHub
parent f441a7c008
commit d80a3ea983
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GPG Key ID: 4AEE18F83AFDEB23
1 changed files with 34 additions and 3 deletions
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37
src/hb-cff-interp-dict-common.hh
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@ -75,6 +75,37 @@ struct top_dict_values_t : dict_values_t<OPSTR>
unsigned int FDArrayOffset; unsigned int FDArrayOffset;
}; };
/* Compile time calculating 10^n for n = 2^i */
constexpr double
pow10_of_2i (unsigned int n)
{
return n == 1 ? 10. : pow10_of_2i (n >> 1) * pow10_of_2i (n >> 1);
}
static const double powers_of_10[] =
{
pow10_of_2i (0x100),
pow10_of_2i (0x80),
pow10_of_2i (0x40),
pow10_of_2i (0x20),
pow10_of_2i (0x10),
pow10_of_2i (0x8),
pow10_of_2i (0x4),
pow10_of_2i (0x2),
pow10_of_2i (0x1),
};
/* Works for x < 512 */
inline double
_hb_pow10 (unsigned int x)
{
unsigned int mask = 0x100; /* Should be same with the first element */
unsigned long result = 1;
const double *power = powers_of_10;
for (; mask; ++power, mask >>= 1) if (mask & x) result *= *power;
return result;
}
struct dict_opset_t : opset_t<number_t> struct dict_opset_t : opset_t<number_t>
{ {
static void process_op (op_code_t op, interp_env_t<number_t>& env) static void process_op (op_code_t op, interp_env_t<number_t>& env)
@ -137,7 +168,7 @@ struct dict_opset_t : opset_t<number_t>
value = (double) (neg ? -int_part : int_part); value = (double) (neg ? -int_part : int_part);
if (frac_count > 0) if (frac_count > 0)
{ {
double frac = (frac_part / pow (10.0, (double) frac_count)); double frac = frac_part / _hb_pow10 (frac_count);
if (neg) frac = -frac; if (neg) frac = -frac;
value += frac; value += frac;
} }
@ -153,9 +184,9 @@ struct dict_opset_t : opset_t<number_t>
if (exp_part != 0) if (exp_part != 0)
{ {
if (exp_neg) if (exp_neg)
value /= pow (10.0, (double) exp_part); value /= _hb_pow10 (exp_part);
else else
value *= pow (10.0, (double) exp_part); value *= _hb_pow10 (exp_part);
} }
return value; return value;