chore(core): fix noise generation which could overflow the custom mod…

…ulus

- updated some function name (for modulus checking) to be clearer on what
they do and when to use them

tfhe/src/core_crypto/algorithms/misc.rs

@@ -108,9 +108,30 @@ pub fn torus_modular_diff<T: UnsignedInteger>(
     }
 }
 
+/// Compute the distance over the torus, taking the absolute value of the smallest distance between
+/// two torus values.
+pub fn modular_distance<T: UnsignedInteger>(first: T, other: T) -> T {
+    let d0 = first.wrapping_sub(other);
+    let d1 = other.wrapping_sub(first);
+    d0.min(d1)
+}
+
+/// Compute the distance over the torus, taking the absolute value of the smallest distance between
+/// two torus values, considering a non native modulus.
+///
+/// # Note
+///
+/// first and other must already be in `0..custom_modulus`.
+pub fn modular_distance_custom_mod<T: UnsignedInteger>(first: T, other: T, custom_modulus: T) -> T {
+    let d0 = first.wrapping_sub_custom_mod(other, custom_modulus);
+    let d1 = other.wrapping_sub_custom_mod(first, custom_modulus);
+    d0.min(d1)
+}
+
 // Our representation of non native power of 2 moduli puts the information in the MSBs and leaves
 // the LSBs empty, this is what this function is checking
-pub fn check_content_respects_mod<Scalar: UnsignedInteger, Input: AsRef<[Scalar]>>(
+#[track_caller]
+pub fn check_encrypted_content_respects_mod<Scalar: UnsignedInteger, Input: AsRef<[Scalar]>>(
     input: &Input,
     modulus: CiphertextModulus<Scalar>,
 ) -> bool {
@@ -132,6 +153,20 @@ pub fn check_content_respects_mod<Scalar: UnsignedInteger, Input: AsRef<[Scalar]
     }
 }
 
+#[track_caller]
+pub fn check_clear_content_respects_mod<Scalar: UnsignedInteger, Input: AsRef<[Scalar]>>(
+    input: &Input,
+    modulus: CiphertextModulus<Scalar>,
+) -> bool {
+    if modulus.is_native_modulus() {
+        true
+    } else {
+        let scalar_modulus: Scalar = modulus.get_custom_modulus().cast_into();
+
+        input.as_ref().iter().all(|&x| x < scalar_modulus)
+    }
+}
+
 /// This function converts an unsigned integer to a float value but does so selecting the truncated
 /// value of the input integer, meaning it will not try to round to the closest representable
 /// integer by the floating point type, it will always select the closest representable integer by

tfhe/src/core_crypto/algorithms/test/ggsw_encryption.rs

@@ -223,7 +223,10 @@ fn ggsw_encrypt_decrypt_custom_mod<Scalar: UnsignedTorus>(params: TestParams<Sca
                 &mut rsc.encryption_random_generator,
             );
 
-            assert!(check_content_respects_mod(&ggsw, ciphertext_modulus));
+            assert!(check_encrypted_content_respects_mod(
+                &ggsw,
+                ciphertext_modulus
+            ));
 
             let decoded = decrypt_constant_ggsw_ciphertext(&glwe_sk, &ggsw);
 
@@ -285,7 +288,10 @@ fn ggsw_par_encrypt_decrypt_custom_mod<Scalar: UnsignedTorus + Send + Sync>(
                 &mut rsc.encryption_random_generator,
             );
 
-            assert!(check_content_respects_mod(&ggsw, ciphertext_modulus));
+            assert!(check_encrypted_content_respects_mod(
+                &ggsw,
+                ciphertext_modulus
+            ));
 
             let decoded = decrypt_constant_ggsw_ciphertext(&glwe_sk, &ggsw);
 
@@ -348,7 +354,10 @@ fn ggsw_seeded_encrypt_decrypt_custom_mod<Scalar: UnsignedTorus>(params: TestPar
 
             let ggsw = seeded_ggsw.decompress_into_ggsw_ciphertext();
 
-            assert!(check_content_respects_mod(&ggsw, ciphertext_modulus));
+            assert!(check_encrypted_content_respects_mod(
+                &ggsw,
+                ciphertext_modulus
+            ));
 
             let decoded = decrypt_constant_ggsw_ciphertext(&glwe_sk, &ggsw);
 
@@ -413,7 +422,10 @@ fn ggsw_seeded_par_encrypt_decrypt_custom_mod<Scalar: UnsignedTorus + Sync + Sen
 
             let ggsw = seeded_ggsw.decompress_into_ggsw_ciphertext();
 
-            assert!(check_content_respects_mod(&ggsw, ciphertext_modulus));
+            assert!(check_encrypted_content_respects_mod(
+                &ggsw,
+                ciphertext_modulus
+            ));
 
             let decoded = decrypt_constant_ggsw_ciphertext(&glwe_sk, &ggsw);
 

tfhe/src/core_crypto/algorithms/test/glwe_encryption.rs

@@ -38,7 +38,10 @@ fn glwe_encrypt_assign_decrypt_custom_mod<Scalar: UnsignedTorus>(params: TestPar
                 &mut rsc.encryption_random_generator,
             );
 
-            assert!(check_content_respects_mod(&glwe, ciphertext_modulus));
+            assert!(check_encrypted_content_respects_mod(
+                &glwe,
+                ciphertext_modulus
+            ));
 
             let mut plaintext_list =
                 PlaintextList::new(Scalar::ZERO, PlaintextCount(glwe.polynomial_size().0));
@@ -101,7 +104,10 @@ fn glwe_encrypt_decrypt_custom_mod<Scalar: UnsignedTorus>(params: TestParams<Sca
                 &mut rsc.encryption_random_generator,
             );
 
-            assert!(check_content_respects_mod(&glwe, ciphertext_modulus));
+            assert!(check_encrypted_content_respects_mod(
+                &glwe,
+                ciphertext_modulus
+            ));
 
             let mut plaintext_list =
                 PlaintextList::new(Scalar::ZERO, PlaintextCount(glwe.polynomial_size().0));
@@ -168,7 +174,10 @@ fn glwe_list_encrypt_decrypt_custom_mod<Scalar: UnsignedTorus>(params: TestParam
                 &mut rsc.encryption_random_generator,
             );
 
-            assert!(check_content_respects_mod(&glwe_list, ciphertext_modulus));
+            assert!(check_encrypted_content_respects_mod(
+                &glwe_list,
+                ciphertext_modulus
+            ));
 
             let mut plaintext_list = PlaintextList::new(
                 Scalar::ZERO,
@@ -226,7 +235,10 @@ fn glwe_trivial_encrypt_decrypt_custom_mod<Scalar: UnsignedTorus>(params: TestPa
 
             trivially_encrypt_glwe_ciphertext(&mut glwe, &plaintext_list);
 
-            assert!(check_content_respects_mod(&glwe, ciphertext_modulus));
+            assert!(check_encrypted_content_respects_mod(
+                &glwe,
+                ciphertext_modulus
+            ));
 
             let mut plaintext_list =
                 PlaintextList::new(Scalar::ZERO, PlaintextCount(glwe.polynomial_size().0));
@@ -280,7 +292,10 @@ fn glwe_allocate_trivial_encrypt_decrypt_custom_mod<Scalar: UnsignedTorus>(
                 ciphertext_modulus,
             );
 
-            assert!(check_content_respects_mod(&ct, ciphertext_modulus));
+            assert!(check_encrypted_content_respects_mod(
+                &ct,
+                ciphertext_modulus
+            ));
 
             let mut output_plaintext_list =
                 PlaintextList::new(Scalar::ZERO, PlaintextCount(polynomial_size.0));
@@ -341,11 +356,14 @@ fn glwe_seeded_encrypt_decrypt_custom_mod<Scalar: UnsignedTorus>(params: TestPar
                 rsc.seeder.as_mut(),
             );
 
-            assert!(check_content_respects_mod(&seeded_glwe, ciphertext_modulus));
+            assert!(check_encrypted_content_respects_mod(
+                &seeded_glwe,
+                ciphertext_modulus
+            ));
 
             let decompressed_glwe = seeded_glwe.decompress_into_glwe_ciphertext();
 
-            assert!(check_content_respects_mod(
+            assert!(check_encrypted_content_respects_mod(
                 &decompressed_glwe,
                 ciphertext_modulus
             ));
@@ -418,7 +436,7 @@ fn glwe_seeded_list_encrypt_decrypt_custom_mod<Scalar: UnsignedTorus>(params: Te
                 rsc.seeder.as_mut(),
             );
 
-            assert!(check_content_respects_mod(
+            assert!(check_encrypted_content_respects_mod(
                 &glwe_seeded_list,
                 ciphertext_modulus
             ));