[Mesa-dev] [PATCH] mesa: Add abs input modifier to base for POW in ffvertex_prog

[Daniel Scharrer]

The result of POW for a negative base is undefined. Even when the result
is multiplied by zero (which is the case here whenever the base is
negative), the Inf and NaNs can propagate past that.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=91342
Signed-off-by: Daniel Scharrer <daniel at constexpr.org>
Cc: "10.6 11.0" <mesa-stable at lists.freedesktop.org>
---
 src/mesa/main/ffvertex_prog.c | 17 ++++++++++++++---
 1 file changed, 14 insertions(+), 3 deletions(-)

diff --git a/src/mesa/main/ffvertex_prog.c b/src/mesa/main/ffvertex_prog.c
index 95b428d..a6183b4 100644
--- a/src/mesa/main/ffvertex_prog.c
+++ b/src/mesa/main/ffvertex_prog.c
@@ -293,9 +293,10 @@ struct ureg {
    GLuint file:4;
    GLint idx:9;      /* relative addressing may be negative */
                      /* sizeof(idx) should == sizeof(prog_src_reg::Index) */
+   GLuint abs:1;
    GLuint negate:1;
    GLuint swz:12;
-   GLuint pad:6;
+   GLuint pad:5;
 };
 
 
@@ -324,6 +325,7 @@ static const struct ureg undef = {
    0,
    0,
    0,
+   0,
    0
 };
 
@@ -342,6 +344,7 @@ static struct ureg make_ureg(GLuint file, GLint idx)
    struct ureg reg;
    reg.file = file;
    reg.idx = idx;
+   reg.abs = 0;
    reg.negate = 0;
    reg.swz = SWIZZLE_NOOP;
    reg.pad = 0;
@@ -350,6 +353,14 @@ static struct ureg make_ureg(GLuint file, GLint idx)
 
 
 
+static struct ureg absolute( struct ureg reg )
+{
+   reg.abs = 1;
+   reg.negate = 0;
+   return reg;
+}
+
+
 static struct ureg negate( struct ureg reg )
 {
    reg.negate ^= 1;
@@ -526,8 +537,8 @@ static void emit_arg( struct prog_src_register *src,
    src->File = reg.file;
    src->Index = reg.idx;
    src->Swizzle = reg.swz;
+   src->Abs = reg.abs;
    src->Negate = reg.negate ? NEGATE_XYZW : NEGATE_NONE;
-   src->Abs = 0;
    src->RelAddr = 0;
    /* Check that bitfield sizes aren't exceeded */
    assert(src->Index == reg.idx);
@@ -953,7 +964,7 @@ static struct ureg calculate_light_attenuation( struct tnl_program *p,
 
       emit_op2(p, OPCODE_DP3, spot, 0, negate(VPpli), spot_dir_norm);
       emit_op2(p, OPCODE_SLT, slt, 0, swizzle1(spot_dir_norm,W), spot);
-      emit_op2(p, OPCODE_POW, spot, 0, spot, swizzle1(attenuation, W));
+      emit_op2(p, OPCODE_POW, spot, 0, absolute(spot), swizzle1(attenuation, W));
       emit_op2(p, OPCODE_MUL, att, 0, slt, spot);
 
       release_temp(p, spot);
-- 
2.6.0