Commit 784c4546 authored by Juan Suárez Romero's avatar Juan Suárez Romero Committed by Marge Bot

nir/lower_double_ops: add note for lowering mod

Add a note to clarify that while Vulkan allows mod(x,y) to be in [0, y]
range, OpenGL does not allow it, so the lowering ensures the result is
always in [0, y) range, as this lowering is shared by the Vulkan and
OpenGL implementation.
Reviewed-by: default avatarElie Tournier <elie.tournier@collabora.com>
Tested-by: Marge Bot <!3315>
Part-of: <!3315>
parent d2e4435c
Pipeline #112792 passed with stages
in 21 minutes and 47 seconds
......@@ -427,6 +427,10 @@ lower_mod(nir_builder *b, nir_ssa_def *src0, nir_ssa_def *src1)
* If the division is lowered, it could add some rounding errors that make
* floor() to return the quotient minus one when x = N * y. If this is the
* case, we return zero because mod(x, y) output value is [0, y).
*
* Worth to note that Vulkan allows the output value to be in range [0, y],
* so mod(x, y) could return y; but as OpenGL does not allow this, we add
* the extra instruction to ensure the value is always in [0, y).
*/
nir_ssa_def *floor = nir_ffloor(b, nir_fdiv(b, src0, src1));
nir_ssa_def *mod = nir_fsub(b, src0, nir_fmul(b, src1, floor));
......
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