SkXPS: clean up SkConstexprMath

src/xps/SkConstexprMath.h

Index: src/xps/SkConstexprMath.h
diff --git a/src/xps/SkConstexprMath.h b/src/xps/SkConstexprMath.h
index 9625d5112b13b492952113fc9d25af8678037c14..0383ab3e67898505565f48c6088933788e926c4e 100644
--- a/src/xps/SkConstexprMath.h
+++ b/src/xps/SkConstexprMath.h
@@ -8,47 +8,24 @@
 #ifndef SkConstexprMath_DEFINED
 #define SkConstexprMath_DEFINED
 
-#include "SkTypes.h"
-#include <limits.h>
+#include <stdint.h>
+#include <limits>
 
-template <uintmax_t N, uintmax_t B>
-struct SK_LOG {
-    //! Compile-time constant ceiling(logB(N)).
-    static const uintmax_t value = 1 + SK_LOG<N/B, B>::value;
-};
-template <uintmax_t B>
-struct SK_LOG<1, B> {
-    static const uintmax_t value = 0;
-};
-template <uintmax_t B>
-struct SK_LOG<0, B> {
-    static const uintmax_t value = 0;
-};
+/** Compile-time constant floor(log_{b}(n)) */

[bungeman-skia, 2016/05/23 15:04:49]

We don't want floor, we want ceiling. I think that's what the adding 1 is for. I
think this is broken for '1', but was required for the simple form.

[hal.canary, 2016/05/23 16:55:39]

function deleted.

+constexpr size_t SkLog(uintmax_t n, uintmax_t b) {
+    return n <= 1 ? 0 : 1 + SkLog(n / b, b);
+}
 
-template<uintmax_t N>
-struct SK_2N1 {
-    //! Compile-time constant (2^N)-1.
-    static const uintmax_t value = (SK_2N1<N-1>::value << 1) + 1;
-};
-template<>
-struct SK_2N1<1> {
-    static const uintmax_t value = 1;
-};
-
-/** Compile-time constant number of base n digits in type t
-    if the bits of type t are considered as unsigned base two.
-*/
-#define SK_BASE_N_DIGITS_IN(n, t) (\
-    SK_LOG<SK_2N1<(sizeof(t) * CHAR_BIT)>::value, n>::value\
-)
 /** Compile-time constant number of base 10 digits in type t

[bungeman-skia, 2016/05/23 15:04:49]

nit: 'type T'

(capitalized, since that's how its actually written.)

[hal.canary, 2016/05/23 16:55:39]

function deleted

-    if the bits of type t are considered as unsigned base two.
-*/
-#define SK_DIGITS_IN(t) SK_BASE_N_DIGITS_IN(10, (t))
+    if the bits of type t are considered as unsigned base two. */
+template <typename T>
+constexpr size_t SkDigitsIn() {

[bungeman-skia, 2016/05/23 15:04:49]

Actually, now that I look, "std::numeric_limits::digits10 + 1" seems to be the
value we're after, and comes in constexpr. Can we use that instead?

[hal.canary, 2016/05/23 16:55:39]

Done.

+    return SkLog(std::numeric_limits<T>::max(), 10);
+}
 
-// Compile-time constant maximum value of two unsigned values.
-template <uintmax_t a, uintmax_t b> struct SkTUMax {
-    static const uintmax_t value = (b < a) ? a : b;
-};
+/** Compile-time constant maximum value of two size_t. */
+constexpr size_t SkSMax(size_t a, size_t b) {

[bungeman-skia, 2016/05/23 15:04:49]

If this is just used for size_t, just use SkTMax directly.

[hal.canary, 2016/05/23 16:55:39]

Done.

+    return b < a ? a : b;
+}
 
 #endif