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Some more RNG Error fixes #270

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Merged
ciaranra merged 3 commits into from
Mar 21, 2026
Merged

Some more RNG Error fixes #270

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5b8a9ae
fixed some more error codes for rng
Jonhas-qtm Mar 18, 2026
06ac49b
called just lint-fix and responded to feedback
Jonhas-qtm Mar 20, 2026
f51bbae
added docstring to new test case
Jonhas-qtm Mar 20, 2026
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41 changes: 23 additions & 18 deletions crates/pecos-qasm/src/engine.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -1238,15 +1238,16 @@ impl QASMEngine {
match name {
"RNGseed" => {
if args.len() != 1 {
return Err(PecosError::ParseInvalidExpression(
"Expected a single seed for RNGseed. Received {args.len()}".to_string(),
));
return Err(PecosError::ParseInvalidExpression(format!(
"RNGseed expects exactly 1 argument (seed), got {}",
args.len()
)));
}
let seed: u64 = match &args[0] {
Expression::Integer(bit_vec) => bit_vec.load(),
_ => {
return Err(PecosError::ParseInvalidExpression(
"Invalid seed for RNGseed. Expected u64".to_string(),
"RNGseed expects a u64 as its argument".to_string(),
));
}
};
Expand All @@ -1256,15 +1257,16 @@ impl QASMEngine {
}
"RNGindex" => {
if args.len() != 1 {
return Err(PecosError::ParseInvalidExpression(
"Expected a single index for RNGseed. Received {args.len()}".to_string(),
));
return Err(PecosError::ParseInvalidExpression(format!(
"RNGindex expects exactly 1 argument (index), got {}",
args.len()
)));
}
let idx: u64 = match &args[0] {
Expression::Integer(bit_vec) => bit_vec.load(),
_ => {
return Err(PecosError::ParseInvalidExpression(
"Invalid idx for RNGindex. Expected u64".to_string(),
"RNGindex expects a u64 as its argument".to_string(),
));
}
};
Expand All @@ -1273,15 +1275,16 @@ impl QASMEngine {
}
"RNGbound" => {
if args.len() != 1 {
return Err(PecosError::ParseInvalidExpression(
"Expected a single bound for RNGbound. Received {args.len()}".to_string(),
));
return Err(PecosError::ParseInvalidExpression(format!(
"RNGbound expects exactly 1 argument (bound), got {}",
args.len()
)));
}
let ubound: u32 = match &args[0] {
Expression::Integer(bit_vec) => bit_vec.load(),
_ => {
return Err(PecosError::ParseInvalidExpression(
"Invalid idx for RNGindex. Expected u64".to_string(),
"RNGbound expects a u32 as its argument".to_string(),
));
}
};
Expand All @@ -1290,10 +1293,12 @@ impl QASMEngine {
}
"RNGnum" => {
if !args.is_empty() {
return Err(PecosError::ParseInvalidExpression(
"RNGnum receives no arguments. Received {args.len()}".to_string(),
));
return Err(PecosError::ParseInvalidExpression(format!(
"RNGnum expects no arguments, got {}",
args.len()
)));
}

let rng_num = self.rng_model.rng_num();

// convert random number to bitvec
Expand All @@ -1303,9 +1308,9 @@ impl QASMEngine {
}
Ok(ExpressionValue::BitVec(bitvec))
}
_ => Err(PecosError::ParseInvalidExpression(
"Invalid RNG function '{name}'".to_string(),
)),
_ => Err(PecosError::ParseInvalidExpression(format!(
"Unknown RNG function '{name}'"
))),
}
}

Expand Down
8 changes: 4 additions & 4 deletions python/quantum-pecos/src/pecos/engines/cvm/rng_model.py
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Original file line number Diff line number Diff line change
Expand Up @@ -31,7 +31,7 @@ def __init__(

def __str__(self) -> str:
"""Returns the str representation of the model."""
return f"RNG Model with bound {self.current_bound} with count {self.count}"
return f"RNG Model bounded by {self.current_bound} with current count {self.count}"

def set_seed(self, seed: int) -> None:
"""Setting the seed for generating random numbers."""
Expand All @@ -54,8 +54,8 @@ def set_index(self, index: int) -> None:
The number after from the stream will be the idx of interest.
"""
if self.count > index:
error_msg = "rngindex called after specified already generated"
raise BufferError(error_msg)
error_msg = f"RNGindex({index}) cannot move backward: current stream index is {self.count}"
raise ValueError(error_msg)
while self.count < index:
self.rng_random()

Expand Down Expand Up @@ -97,5 +97,5 @@ def eval_func(self, params: dict, output: dict) -> None:
binary_val = BitUInt(creg.size, rng)
creg.set(binary_val)
else:
error_msg = f"RNG function not supported {func_name}"
error_msg = f"Unknown RNG Function '{func_name}'"
raise ValueError(error_msg)
14 changes: 14 additions & 0 deletions python/quantum-pecos/tests/pecos/unit/test_rng.py
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Original file line number Diff line number Diff line change
Expand Up @@ -33,6 +33,20 @@ def test_bounded_random() -> None:
assert 0 <= random_number < bound


def test_set_idx_raises_for_backwards_index() -> None:
"""Verifies that an error is raised when specifying an index that was already consumed in the RNG stream."""
rng = RNGModel(shot_id=0)
rng.set_seed(42)

rng.set_index(4)

try:
rng.set_index(3)
except ValueError as exc:
expected_error_msg = "RNGindex(3) cannot move backward: current stream index is 4"
assert str(exc) == expected_error_msg


def test_set_idx() -> None:
"""Verifies that the idx is set properly for our model."""
rng = RNGModel(shot_id=0)
Expand Down
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