vtn: Fix Modf.

We were botching this for negative numbers - floor of a negative rounds
the wrong way.  Additionally, both results are supposed to retain the
sign of the original.

To fix this, just take the abs of both values, then put the sign back.
There's probably a better way to do this, but this works for now.

1 files changed, 8 insertions, 4 deletions

diff --git a/src/glsl/nir/spirv/vtn_glsl450.c b/src/glsl/nir/spirv/vtn_glsl450.c
index 515a743fe48..b98ef052cbf 100644
--- a/src/glsl/nir/spirv/vtn_glsl450.c
+++ b/src/glsl/nir/spirv/vtn_glsl450.c
@@ -418,16 +418,20 @@ handle_glsl450_alu(struct vtn_builder *b, enum GLSLstd450 entrypoint,
    case GLSLstd450InverseSqrt: op = nir_op_frsq;       break;
 
    case GLSLstd450Modf: {
-      val->ssa->def = nir_ffract(nb, src[0]);
+      nir_ssa_def *sign = nir_fsign(nb, src[0]);
+      nir_ssa_def *abs = nir_fabs(nb, src[0]);
+      val->ssa->def = nir_fmul(nb, sign, nir_ffract(nb, abs));
       nir_store_deref_var(nb, vtn_nir_deref(b, w[6]),
-                          nir_ffloor(nb, src[0]), 0xf);
+                          nir_fmul(nb, sign, nir_ffloor(nb, abs)), 0xf);
       return;
    }
 
    case GLSLstd450ModfStruct: {
+      nir_ssa_def *sign = nir_fsign(nb, src[0]);
+      nir_ssa_def *abs = nir_fabs(nb, src[0]);
       assert(glsl_type_is_struct(val->ssa->type));
-      val->ssa->elems[0]->def = nir_ffract(nb, src[0]);
-      val->ssa->elems[1]->def = nir_ffloor(nb, src[0]);
+      val->ssa->elems[0]->def = nir_fmul(nb, sign, nir_ffract(nb, abs));
+      val->ssa->elems[1]->def = nir_fmul(nb, sign, nir_ffloor(nb, abs));
       return;
    }