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concrete/docs/compilation/composition.md
2024-08-26 16:17:01 +02:00

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# Combining compiled functions with the composable flag
This document explains how to combine compiled functions with the `composable` flag in **Concrete**.
By setting the `composable` flag to `True`, you can compile a function such that its outputs can be reused as inputs. For example, you can then easily compute `f(f(x))` or `f**i(x) = f(f(...(f(x) ..))` for a non-encrypted integer `i` variable, which is usually required for recursions.
Here is an example:
```python
from concrete import fhe
@fhe.compiler({"counter": "encrypted"})
def increment(counter):
return (counter + 1) % 100
print("Compiling `increment` function")
increment_fhe = increment.compile(list(range(0, 100)), composable=True)
print("Generating keyset ...")
increment_fhe.keygen()
print("Encrypting the initial counter value")
counter = 0
counter_enc = increment_fhe.encrypt(counter)
print(f"| iteration || decrypted | cleartext |")
for i in range(10):
counter_enc = increment_fhe.run(counter_enc)
counter = increment(counter)
# For demo purpose; no decryption is needed.
counter_dec = increment_fhe.decrypt(counter_enc)
print(f"| {i} || {counter_dec:<9} | {counter:<9} |")
```
Remark that this option is the equivalent to using the `fhe.AllComposable` policy of [modules](composing_functions_with_modules.md). In particular, the same limitations may occur (see [limitations documentation](composing_functions_with_modules.md#limitations) section).