X-Git-Url: https://git.libre-soc.org/?a=blobdiff_plain;f=src%2Futil%2Ffast_idiv_by_const.h;h=638b52a3ffbb8428adc7066429ae87a363bf8dbd;hb=a4c708dd24e5ba8ac381973c14db8d23f4ac97bf;hp=1ba9f9a20b8279d022f809885a497f9df115067f;hpb=64eb0738d4e35e9ceb4bf99b028bdd5e12c59c34;p=mesa.git

diff --git a/src/util/fast_idiv_by_const.h b/src/util/fast_idiv_by_const.h
index 1ba9f9a20b8..638b52a3ffb 100644
--- a/src/util/fast_idiv_by_const.h
+++ b/src/util/fast_idiv_by_const.h
@@ -36,10 +36,6 @@
 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.
@@ -68,19 +64,19 @@ typedef uint32_t uint_t;
  */
 
 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
@@ -102,8 +98,8 @@ util_compute_fast_sdiv_info(sint_t D);
  *   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
@@ -120,7 +116,7 @@ util_compute_fast_sdiv_info(sint_t D);
  */
 
 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
@@ -128,7 +124,7 @@ struct util_fast_udiv_info {
 };
 
 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.
@@ -139,7 +135,13 @@ static inline uint32_t
 util_fast_udiv32(uint32_t n, struct util_fast_udiv_info info)
 {
    n = n >> info.pre_shift;
-   /* For non-power-of-two divisors, use a 32-bit ADD that clamps to UINT_MAX. */
+   /* 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;