extern "C" {
#endif
-/* You can set these to different types to get different precision. */
-typedef int32_t sint_t;
-typedef uint32_t uint_t;
-
/* Computes "magic info" for performing signed division by a fixed integer D.
* The type 'sint_t' is assumed to be defined as a signed integer type large
* enough to hold both the dividend and the divisor.
*/
struct util_fast_sdiv_info {
- sint_t multiplier; /* the "magic number" multiplier */
+ int64_t multiplier; /* the "magic number" multiplier */
unsigned shift; /* shift for the dividend after multiplying */
};
struct util_fast_sdiv_info
-util_compute_fast_sdiv_info(sint_t D);
+util_compute_fast_sdiv_info(int64_t D, unsigned SINT_BITS);
/* Computes "magic info" for performing unsigned division by a fixed positive
- * integer D. The type 'uint_t' is assumed to be defined as an unsigned
- * integer type large enough to hold both the dividend and the divisor.
- * num_bits can be set appropriately if n is known to be smaller than
- * the largest uint_t; if this is not known then pass
- * "(sizeof(uint_t) * CHAR_BIT)" for num_bits.
+ * integer D. UINT_BITS is the bit size at which the final "magic"
+ * calculation will be performed; it is assumed to be large enough to hold
+ * both the dividand and the divisor. num_bits can be set appropriately if n
+ * is known to be smaller than calc_bits; if this is not known then UINT_BITS
+ * for num_bits.
*
* Assume we have a hardware register of width UINT_BITS, a known constant D
* which is not zero and not a power of 2, and a variable n of width num_bits
* emit("result >>>= UINT_BITS")
* if m.post_shift > 0: emit("result >>>= m.post_shift")
*
- * The shifts by UINT_BITS may be "free" if the high half of the full multiply
- * is put in a separate register.
+ * This second version works even if D is 1. The shifts by UINT_BITS may be
+ * "free" if the high half of the full multiply is put in a separate register.
*
* saturated_increment(n) means "increment n unless it would wrap to 0," i.e.
* if n == (1 << UINT_BITS)-1: result = n
*/
struct util_fast_udiv_info {
- uint_t multiplier; /* the "magic number" multiplier */
+ uint64_t multiplier; /* the "magic number" multiplier */
unsigned pre_shift; /* shift for the dividend before multiplying */
unsigned post_shift; /* shift for the dividend after multiplying */
int increment; /* 0 or 1; if set then increment the numerator, using one of
};
struct util_fast_udiv_info
-util_compute_fast_udiv_info(uint_t D, unsigned num_bits);
+util_compute_fast_udiv_info(uint64_t D, unsigned num_bits, unsigned UINT_BITS);
+
+/* Below are possible options for dividing by a uniform in a shader where
+ * the divisor is constant but not known at compile time.
+ */
+
+/* Full version. */
+static inline uint32_t
+util_fast_udiv32(uint32_t n, struct util_fast_udiv_info info)
+{
+ n = n >> info.pre_shift;
+ /* If the divisor is not 1, you can instead use a 32-bit ADD that clamps
+ * to UINT_MAX. Dividing by 1 needs the full 64-bit ADD.
+ *
+ * If you have unsigned 64-bit MAD with 32-bit inputs, you can do:
+ * increment = increment ? multiplier : 0; // on the CPU
+ * (n * multiplier + increment) // on the GPU using unsigned 64-bit MAD
+ */
+ n = (((uint64_t)n + info.increment) * info.multiplier) >> 32;
+ n = n >> info.post_shift;
+ return n;
+}
+
+/* A little more efficient version if n != UINT_MAX, i.e. no unsigned
+ * wraparound in the computation.
+ */
+static inline uint32_t
+util_fast_udiv32_nuw(uint32_t n, struct util_fast_udiv_info info)
+{
+ assert(n != UINT32_MAX);
+ n = n >> info.pre_shift;
+ n = n + info.increment;
+ n = ((uint64_t)n * info.multiplier) >> 32;
+ n = n >> info.post_shift;
+ return n;
+}
+
+/* Even faster version but both operands must be 31-bit unsigned integers
+ * and the divisor must be greater than 1.
+ *
+ * info must be computed with num_bits == 31.
+ */
+static inline uint32_t
+util_fast_udiv32_u31_d_not_one(uint32_t n, struct util_fast_udiv_info info)
+{
+ assert(info.pre_shift == 0);
+ assert(info.increment == 0);
+ n = ((uint64_t)n * info.multiplier) >> 32;
+ n = n >> info.post_shift;
+ return n;
+}
#ifdef __cplusplus
} /* extern C */
projects / mesa.git / blobdiff